Green’s Dictionary of Slang

1. £5, a £5 note.

1868		‘Six Years in the Prisons of England’ in Temple Bar Mag. Nov. 538: ‘What are fins?’ ‘Five-pound notes, or flash notes.’.
1879		‘Autobiog. of a Thief’ in Macmillan’s Mag. (London) XL 503: About two moon after this the same fence fell for buying two finns (£5 notes), for which he got a stretch and a half.
1887		‘Dagonet’ ‘A Plank Bed Ballad’ in Referee 12 Feb. n.p.: One day I’d a spree with two finns in my brig, / And a toy and a tackle – both red ’uns.
1895		Western Champion (Barcaldine) 31 Dec. 9/5: A profitable profession it seemed, too, judging from the cool way they talked of ‘John Dunns’ (£l), ‘thick ’uns’ (sovs.), ‘canarys’ (halfsovs.), ‘finn’ (£5), &c [AND].
1906		D. Stewart Vultures of the City in Illus. Police News 15 Dec. 12/1: ‘He collared a finney (five pound note) out his cly (pocket) and bundled the cove into the coal hole’.
1907		Sun. Times (Perth) 5 May 4/7: ‘Have a tid,’ the punter grins, / When the book he’s been awaiting / Comes to light with fifty fins.
1914		Truth (Melbourne) 6 June 2/4: I’ll bet a ‘fin,’ they weren’t taught those slangy words at school.

2. (US, also finski, fin-spot, pfinif) a $1 or, more commonly, $5 bill.

1909		F.H. Tillotson How I Became a Detective 89: A ‘pfinif’ is a five-dollar bill.
1927		K. Nicholson Barker 149: Fin – A dollar bill.
1935		N. Algren ‘If You Must Use Profanity’ in Texas Stories (1995) 46: You walked to Montgomery — unless you had a fin.
1938		Reading (PA) Eagle 20 Mar. 7/3: A five dollar bill is a ’finskie’ a nickel is a ‘jit’ and a half a dollar is ‘half a schnooze’ ‘half a schmier’ or a ‘half a rock’.
1947		J.F. Bardin Last of Philip Banter in Bardin Omnibus (1976) 253: I’d rather do without an extra finn at Christmas.
1953		‘John Eagle’ Hoodlums (2021) 69: ‘You’re not leaving until I get a fin’.
1959		M. Richler Apprenticeship of Duddy Kravitz (1964) 23: Only ten years ago he would have had to sweat blood before he coulda raised a lousy fin.
1964		H. Selby Jr Last Exit to Brooklyn 29: I’ll only charge ya a fin.
1976		Cab Calloway Of Minnie the Moocher and Me 182: Mash me a fin, gate, so I can cop me a fry.
1987		W.T. Vollmann You Bright and Risen Angels (1988) 313: They won’t have nary a fin or a sawbuck to get home on.
1991		(con. 1920s) O.D. Brooks Legs 118: ‘Deuce, hell,’ he told me, ‘here’s a fin.’.
1996		Eble Sl. and Sociability 76: The only foreign language that has contributed more than a sprinkling of slang terms is Yiddish, from which English has borrowed such varied informal vocabulary as fin ‘five dollar bill’.

3. (Aus./Can./US Und.) a prison sentence of five years.

1911		Truth (Brisbane) 22 Jan. 10/4: To the prisoner [...] a sentence of one month is a ‘moon’; of three months a ‘drag’; of six months, a ‘sixer’ or ‘zack’; twelve months a ‘stretch’; and five years a ‘fin.’.
1931		Irwin Amer. Tramp and Und. Sl. 72: Fin [...] a five years’ sentence.
1949		Monteleone Criminal Sl. (rev. edn) 83–4: fin [...] finn A five year prison sentence.
1950		Goldin et al. DAUL 69/1: Fin. [...] 3. Five years in prison.
1962		Ragen & Finston World’s Toughest Prison 798: fin – A five-year sentence, or parole board setting.
1978		R. Caron Go-Boy! 134: A fin eh? I guess that can be a long haul for a boy of your age.
1989		J. Morton Lowspeak.
1992		Bentley & Corbett Prison Sl. 21: Nickel A five-year prison sentence. In prison, the number of years of sentences are often referred to as monetary coin amounts. (Archaic: fin, handful, pound).

4. (US) a throw of five in craps dice.

2001

Word for the Wise 31 Aug. [US radio script] That same drive to rhyme inspired twin fins for a roll of two fives.