Green’s Dictionary of Slang

1. money, usu. in the form of a bribe (cf. oil of palm(s) under oil of... n.).

1624		Middleton Game at Chess III i: Palm-oil will make a pursuivant relent.
1840		London Mag. Mar. 92/1: My system is always, if I get embroiled with a policeman, to slip him a crown. This palm oil [...] softens the asperity of the immaculate peace-preserver.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn) 183: palm oil, money. [Ibid.] 185: palm soap, money.
1867		Bendigo Advertiser (Vic.) 19 July 2/2: [H]e had been informed that he could secure the payment [...] by what is termed in slang phrase ‘palm oil,’ in plain language by bribing those who would hare a voice in dealing with his claim.
1879		C. Dickens Jnr Dict. of London 234: Sight-seeing. The enterprising sight-seer who proceeds on this plan, and who understands the virtues of palm oil, is sure to see everything he cares to see .
1880		W. Hooe Sharping London 35: Palm Oil, money put in the palm of the hand by way of bribe.
1890		Dundee Eve. Teleg. 3 Apr. 2/5: Palm oil [...] such an obviously appropriate name for [money] that ‘shin-plaster’ seems feeble by comparison, and the young but widely popular ‘oof,’ ‘oof-bird,’ and ‘oof-tish’, imbecile.
1894		Truth (Sydney) 13 May. 1/8: There are palmists and palmists, also there are psalm-oilists. The fees of these personages vary.
1894		Truth (Sydney) 25 Nov. 1/3: The wolves began to show their fangs and take revenge for the ‘Palm Oil’ out of which they reckoned they had been defrauded.
1900		Bulletin (Sydney) 29 Dec. 31/4: ‘Palm-oil’ to the police must surely be the reason why there are allowed to exist in Sydney so many so-called ‘registry-offices,’ which carry on a business of a very different character.
1900		‘Ouida’ Massarenes 32: I think she’ll take us up, William [...] but she will want a lot of palm-grease [F&H].
1905		Star (Canterbury) 26 Jan. 2/7: [headline] Political ‘Palm Oil’ Syveton’s safe [...] was found to contains receipts for 1,300,000 francs that had been distributed [...] to promote his various campaigns.
1913		Sport (Adelaide) 28 June 9/2: They Say [...] That The local engine driver is in search of palm oil since he met the apple of his eye.
1918		L.E. Ruggles Navy Explained 102: Sailormen [...] probably coin more words for money than any other body of men [...] Sheckles, iron men, washers, clackers, jack, cart wheels, simoleons, kopex, mazuma, palm grease, evil metal, oro, jingles, liberty, bait, sou, armor, plate, holy stones, joy berries, and many others.
1922		Joyce Ulysses 594: Ask her captain, he advised them, how much palmoil the British Government gave him for that day’s work.
1931		Irwin Amer. Tramp and Und. Sl. 140: Palm Oil.–Money paid as a bribe or for protection against police interference.
1936		C. Woolrich ‘Dilemma of the Dead lady’ in Penzler Pulp Fiction (2007) 47: He saw the fellow counting over the palm-oil, so he handed him the last remaining banknote.
1961		T. Murphy Whistle in the Dark Act I: Too much back-handin’, too much palm-oil.
1989		J. Morton Lowspeak.

2. in attrib. use of sense 1, implying venality.

1899

Star (Canterbury) 14 Jan. 2: The white man is still the palm-oil ruffian of fifty years ago.