"Palestinian" is now applied only to Arabs, as if there is/was a political, social and demographic identity of Arabs as distinctly "Palestinian". Not Syrian. Not Jordanian (more on this later) or any other Arab community.
The Palestinian people, (Arabic: الشعب الفلسطيني, ash-sha`b al-filasTīni) also referred to as Palestinians or Palestinian Arabs (Arabic: الفلسطينيون, al-filasTīnīyyūn; Arabic: العرب الفلسطينيون, al-`Arab al-filasTīnīyyūn), are an Arabic-speaking Mediterranean people with family origins in the geographic region of Palestine.
Taken all together, the object in the usage of "Palestinian Arabs" is first and foremost not connected with Arabs but to negate and deny any Jewish connection or rights to the geographical entity known as the Land of Israel (Eretz-Yisrael).
To his credit,
historian Rashid Khalidi...cautions against the efforts of some Palestinian nationalists to "anachronistically" read back into history a nationalist consciousness that is in fact "relatively modern".
 Khalidi, Palestinian Identity: The Construction of Modern National Consciousness. Columbia University Press. 1997, p. 19–21.
 Khalidi, 1997, p. 149.
In response to this semantic struggle over such a terminology, one response has been to deny in toto the term as in this opinion, that The Palestinian People Do Not Exist:
Way back on March 31, 1977, the Dutch newspaper Trouw published an interview with Palestine Liberation Organization executive committee member Zahir Muhsein. Here's what he said:
The Palestinian people does not exist. The creation of a Palestinian state is only a means for continuing our struggle against the state of Israel for our Arab unity. In reality today there is no difference between Jordanians, Palestinians, Syrians and Lebanese. Only for political and tactical reasons do we speak today about the existence of a Palestinian people, since Arab national interests demand that we posit the existence of a distinct "Palestinian people" to oppose Zionism. For tactical reasons, Jordan, which is a sovereign state with defined borders, cannot raise claims to Haifa and Jaffa, while as a Palestinian, I can undoubtedly demand Haifa, Jaffa, Beer-Sheva and Jerusalem. However, the moment we reclaim our right to all of Palestine, we will not wait even a minute to unite Palestine and Jordan.
That's pretty clear, isn't it?...It demonstrates conclusively that the Palestinian nationhood argument is the real strategic deception – one geared to set up the destruction of Israel.
I've said it before and I will say it again, in the history of the world, Palestine has never existed as a nation. The region known as Palestine was ruled alternately by Rome, by Islamic and Christian crusaders, by the Ottoman Empire and, briefly, by the British after World War I. The British agreed to restore at least part of the land to the Jewish people as their ancestral homeland. It was never ruled by Arabs as a separate nation.
Another element is to ask when did the term come into use. What was its history. Some claim in the early 1920s, especially after the 4th or 5th (1921; 1922) Arab Congresses (see here; and also here). Into the early 1920s, for sure, the local, indigenous Arabs viewed their status as Syrians, and referred to themselves as "Southern Syrians" (see here; ) where it is made clear:
"The first Palestinian Arab congress (al-Muʾtamar al-Arabi al-Filastini) met in Jerusalem from 27 January to 9 February 1919...A majority sought the incorporation of Palestine into an independent Syrian state, and the delegates strongly denounced French claims to a mandate over Syria...The congress issued a statement which included the statement: 'We consider Palestine as part of Arab Syria, as it has never been separated from it at any time. We are connected with it by national, religious, linguistic, natural, economic and geographical bonds.' "
That there was a recognition, even amongst the most nationalist Arabs that two different entities exist can be understood from the Agreement Between Emir Feisal and Dr. Weizmann signed on 3 January, 1919 in the presence of Lawrence of Arabia. "Palestine" was something other than the "Arab State" to be awarded to the Arabs. "Palestine" was for the Jews.
See the text:
His Royal Highness the Emir Feisal, representing and acting on behalf of the Arab Kingdom of Hedjaz, and Dr. Chaim Weizmann, representing and acting on behalf of the Zionist Organization, mindful of the racial kinship and ancient bonds existing between the Arabs and the Jewish people, and realizing that the surest means of working out the consummation of their natural aspirations is through the closest possible collaboration in the development of the Arab State and Palestine, and being desirous further of confirming the good understanding which exists between them, have agreed upon the following:
The Arab State and Palestine in all their relations and undertakings shall be controlled by the most cordial goodwill and understanding, and to this end Arab and Jewish duly accredited agents shall be established and maintained in the respective territories.
Immediately following the completion of the deliberations of the Peace Conference, the definite boundaries between the Arab State and Palestine shall be determined by a Commission to be agreed upon by the parties hereto.
That is fairly clear. Actually, most assuredly so.
I certainly agree that a "Palestinian" Arab nationality used to oppose the Zionist character of the country is a later development, but not in 1964 as some claim. In reviewing historical material, I came across the usage of the term "Palestiian Arabs" early on and specifically as identifying Arabs, as opposed to Jews/Zionists, as "Palestinians". The material is the speeches made in the British Parliament and the House of Lords and shows a political usage of the term. However, it is definitely not clear-cut.
In the first instance, most of the speakers employing the term are anti-Zionists. But not all. In the second instance, while it is used to designate Arabs as opposed to Jews as well as Zionists, the examples I found include the term being used to signify Jews, non-Jews in the area and others.
So, I include below various examples that display that usage but also other usages relating to Jews, Germans or others or any inhabitant/resident of the Palestine Mandate as early as 1918 with many quite obviously denoting Arabs as "Palestinians" and not Jews.
June 25, 1918
Major Earl WINTERTON asked the Secretary of State for Foreign Affairs what facilities have been given to the Palestinian and Syrian political leaders now in Egypt to visit Palestine?
That refers solely to Arabs.
On June 29, 1920
I am quite aware that in many quarters it is extremely bad form to take any interest in former enemy aliens...I have a profound sympathy for any civilians, whether they be of British or German or any other nationality, who have to undergo two years' internment...these Palestinian Germans are being detained by the desire of the Zionists in order that their property in Palestine may be acquired
On April 29, 1920
Gentleman the Member for the City of London (Mr. Balfour) in his famous declaration in December, 1917, in regard to the settlement of Palestine on a Zionist basis...I think, however, that it is most important that two considerations in connection with this settlement should be presented to the House and the country. One is that the rights of the existing Palestinian inhabitants, especially the Moslems and Christians, the resident cultivators, should be carefully safeguarded. The vast majority of the resident cultivators of Palestine are very poor men. Ninety per cent. are either Christian or Moslem. The Jews form less than 10 per cent, of the whole of the inhabitants, and of that 10 per cent. the majority are in the towns engaged in the small retail trade, money-lending and occupations of that kind. Therefore, if there is to be any settlement of Jews from abroad, I think the rights of the existing cultivators must be most carefully safeguarded. I think the House will give a general assent to that proposition.
On June 14, 1921
...do not let us make the same mistake in Palestine as was committed in Mesopotamia two years ago, that is to say, have too many English officials; rather have a less efficient Government, manned by Palestinians, Jews, Christians and Moslems, getting them to work together in the same office...
One word about Trans-Jordania. Across the Jordan you have a real Arab country, and I am delighted that there a settlement has been arrived at. A settlement has been arrived at, for the present at any rate, by having a member of the Sherifian family and by trying to start something like a decent administration. For centuries there have been bloody feuds between the tribes. Their conditions are quite separate. Do not let us create any economic barriers between them. Free trade and eventually federation are absolutely essential. Free intercourse also is absolutely essential.
That quotation employs the term "Palestinian" to refer to all residents of the territory while noting that Transjordan, todays's Hashemite Kingsom of Jordan, is different, it being a "real Arab country", which, then, "Palestine" isn't - because it is a Jewish national home.
From June 8, 1921
The fact is that Palestinians feel that the Zionist grip is rapidly closing upon them, and they are helpless...Zionists are not, seemingly, Palestinians.
On November 2, 1921
...The Government, by holding back certain facts which were then in their possession, have, I believe, done a great injustice to the Palestinians, who stand accused of a rather stupid and wanton pogrom on that occasion [referring to the May riots in Jaffa - YM].
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...Commission proposed sale large plots valuable urban lands impossible for individual Palestinians to purchase, leaving Zionists sole prospective purchasers at the price they fix. What is going on in Palestine now...in my opinion, [is that] injustice is being committed against the Palestinians.
"Palestinians" are those who engaged in violence, therefore, they are the Arabs, not Jews/Zionists.
On June 8 1921
At the present time there are three distinct Jewish Labour Parties in Palestine...The Centre Party is the largest of them, and it advocates nationalisation of the land, and a national life based upon Hebrew. That is a programme which must be abhorrent to all Palestinians, both Moslem and Christian...it employs itself in breaking up Labour processions, and also in trying to convert the Palestinians into Bolsheviks.
"Palestinians', it seems, cannot be Jews.
On June 21, 1922, I found multiple usages:
On more than one occasion he [Winston Churchill, Colonial Secretary] has been asked by Arab Delegations and Palestinian organisations to remove the Zionist bias and to substitute in its place a national system.
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Now, Palestinian organisations have put forward what would appear to be a quite reasonable demand for a share of the control of the immigration of the people that are to come into their own country.
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The Palestinians have asked for an early recognition of self-government in their country and they have been told that it must be very gradual,
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...as we think, the injustices, upon the Palestinians has been already told. We may have told it feebly, but at all events those who took up the cause of the Palestinians were in thorough and complete earnest.
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That Proclamation pledges us in the most direct fashion to the whole Palestinian people, Moslems, Christians and Jews at that time in Palestine
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The Declaration promised that nothing should be done which would prejudice the "civil rights" of the Palestinians. Is it possible to say that we have done nothing which prejudices those civil rights? These rights have been trampled upon ever since the Zionist Commission established itself at Jerusalem. The Administration of Palestine at the present time is distinctly Zionist, and it is Zionist in the sense that it frequently acts in defiance of the unanimous wishes of the people, Moslems, Christians and orthodox Jews. Palestinians would never have objected to the establishment of more colonies of well-selected Jews; but, instead of that, we have dumped down 25,000 promiscuous people on the shores of Palestine, many of them quite unsuited for colonising purposes, and some of them Bolsheviks, who have already shown the most sinister activity. The Arabs would have kept the Holy Land clear from Bolshevism..
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But, far worse than the loss of money, we have lost the confidence of the Palestinian people, who trusted us implicitly when they heard the Declaration which General Allenby made to them...
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It is really a painful and humiliating fact that the Palestinians under Turkish rule were more contented, more lightly taxed, and had far more share in their Government, than they have under the British flag at the present moment...What we have done is, by concessions, not to the Jewish people but to a Zionist extreme section, to start a running sore in the East...
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...to enforce a policy which, I contend, conflicts with the pledges of His Majesty's Government, and also with the elementary rights of the Palestinian people. The Mandate as it stands will undoubtedly, in time, transfer the control of the Holy Land to New York, Berlin, London, Frankfurt and other places. The strings will not be pulled from Palestine; they will be pulled from foreign capitals...
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There is nothing in that speech which will give any degree of confidence either to the Arab Delegation here or to the Palestinians in the East
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Sir Herbert Samuel, at the meeting to which I have referred, said distinctly there was no intention of allowing the Zionist Commission to act as an imperium in imperio, and that they were to be absolutely confined to carrying out the objects which strictly concern the Jews, and not those which concern the Palestinians in general.
All the above usages are varied and go either way.
On May 4, 1922, a question is asked on the proposed Palestine Constitution
Whether English Jews holding official positions in Palestine will be considered as Palestinians, and if so whether Arabs will be equally eligible for such positions...
The answer being:
In any case there is no discrimination in the Palestine Civil Service against Palestinian Arabs who, if they possess the necessary qualifications, may fill vacancies as they occur.
So, Jews can be "Palestinians" above.
On November 29, 1922
If this view is correct, it seems to me clear that the League of Nations was bound by its own Covenant to consult the wishes of the Palestinians before ratifying the Mandate. But so far as I know—and I hope I am wrong—nothing has been done in that direction.
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I allude to the poor Montenegrin people and the Palestinians. In neither of those cases has the League of Nations stood up for the rights of small and unprotected people.
"Palestinians" are separate.
So, obviously, the above primary source material is, in the end, inconclusive. What was found were many usages that fit the contemporary reality of a "Palestinian people" but also other connotations.
There is also this from Malcolm MacDonald in the House debate on November 24, 1938:
I think that this House, which is so capable of a generous understanding of other peoples, ought to recognise that many in the Palestinian Arab movement are moved by a genuine patriotism. However wrong they may be, however misguided they may be, however disastrous their policy may be, many of them have felt compelled to take the risk of laying down their lives for their country.(*)
What is telling, though, is that the Palestine Liberation Organization, founded in 1964, did not fully view its struggle as relating ot the territory controlled by Jordan. For the PLO, "Palestine" was only Israel, again revealing the instrumental nature of the term.
"Palestine" never truly existed as a country, as a geo-political entity that promoted a special culture, a unique ethos, that generated a national identity and, of course, never in any legal form did it exist even under centuries of Muslim rule.
And I found this later elaboration there which is quite relevant to the discussion of a distinct "Palestinian Arab" identity:
I think that this House, which is so capable of a generous understanding of other peoples, ought to recognise that many in the Palestinian Arab movement are moved by a genuine patriotism. However wrong they may be, however misguided they may be, however disastrous their policy may be, many of them have felt compelled to take the risk of laying down their lives for their country.
...The other side is this: the Arabs cannot say that the Jews are driving them out of their country. If not a single Jew had come to Palestine after 1918, I believe the Arab population of Palestine to-day would still have been round about the 600,000 figure at which it had been stable under Turkish rule. It is because the Jews who have come to Palestine bring modern health services and other advantages that Arab men and women who would have been dead are alive to-day, that Arab children who would never have drawn breath have been born and grown strong. It is not only the Jews who have benefited from the Balfour Declaration. They can deny it as much as they like, but materially the Arabs in Palestine have gained very greatly from the Balfour Declaration.
I know that it is useless to press that argument on the Arabs. They are deaf to the argument, they are blind to the spectacle of a gradually improving standard of life for their people, because they are thinking of something else. They are thinking of their freedom. They are afraid that, if this process goes on, then at last they will have to surrender to the political over-lordship of the enterprising, hardworking, ever-increasing citizens of the Jewish National Home. I say that we British people ought to be the last people in the world not to understand the feelings of the Arabs in this matter, because we too would sacrifice material advantages if we thought our freedom was at stake. We cannot put the Jews under the domination of the Arabs in Palestine, but also, unless we can remove that Arab fear that they are going to be put under the domination of the Jews, we shall have to face a suspicious and hostile people over a great area of the Near East, and we shall find that we have to lock up a great part of our Army in Palestine indefinitely.