Green’s Dictionary of Slang

1. a crown, 5s (25p); thus half-Oxford, half-a-crown, 2s 6d (12½p) [dollar n.¹ (1)].

1898		Binstead & Wells Pink ’Un and Pelican 65: In peacocked the little man with the long chain, the ‘wine-steward’ who chucked away Ernest’s ‘half-oxford’.
1919		Tweed Dly (Murwillumbah, NSW) 18 Jan. 7/5: ‘I want five bob in the guts! [...] I wanter noxford scholar in the guts!’.
1932		‘P.P.’ Rhy. Sl. 7: Come on, boys ‘rats and mice,’ who pays for the ‘Joe Skinner’ – it won’t be more than an ‘Oxford’.
1933		Derby Dly Teleg. 7 Aug. 6/3: Professional thieves use such words as [...] sprazey [...] half a tosh [...] Oxford (five shillings), oncer (sovereign).
1943		J.A.W. Bennett ‘Eng. as it is Spoken in N.Z.’ in AS XVIII:2 Apr. 91: ‘Oxford scholar’ is occasionally heard for five shillings; it probably comes from English rhyming slang for ‘dollar.’.
1950		P. Hoskins No Hiding Place! 191/1: Oxford Scolar. (Dollar) five shillings.
1960		J. Franklyn Dict. of Rhy. Sl.
1969		S.T. Kendall Up the Frog 12: Lend us ’arf an Oxford scholar, I’m boracic lint.
1971		‘Jack Jones’ Rhyming Cockney Sl.

2. a collar.

1895		Mirror of Life 27 July 14/2: The hooks soon piped the stranger / With his Oxford scholar high .
1910		Eve. Teleg. (Dundee) 3 Aug. 4/1: He puts on a clean 'Oxford,' changes his 'almonds,' brushes his 'Barnet,' and dons his 'turtles.' He then pays a visit to the 'rub-a-dub'.
1924		Mail (Adelaide) 16 Feb. 1/4: A few of the ways that clothes are referred to:— Collar— Oxford scholar.
1937		L. Lane Me and My Girl I iii: charles: ’Oller boys ’oller? bill: Oxford scholar! charles: Oxford scholar? bill: The arf-a-dollar! (Charles offers him half-a-crown) bill: Naow – the collar!

3. (Aus./N.Z.) $1.

1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxviii 10/1: oxford: Dollar. From Oxford scholar.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 7: ‘Twenty Oxford Scholars is a lot of cabbage for one fluffy duck,’ he said as he mentally calculated how may pig’s ears he could buy with that amount of pelf. [Ibid.] 11: ‘I’ll have a Lily of Laguna and a Tom Thumb chaser please,’ he said to the jump as he casually dropped a couple of Oxfords on the near and far.
1996		Ozwords Oct. 🌐 If you haven’t got an Oxford left, this means you haven’t got a dollar.
2000		R.G. Barrett Leaving Bondi (2013) [ebook] I’ve just earned a few Oxford Scholars tonight.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 132/2: Oxford scholar n. a dollar.
2013		T. Peacock More You Bet 66: A ‘dollar’ in rhyming slang was and is, an ‘Oxford scholar’, or ‘an Oxford’ for short.