Green’s Dictionary of Slang

1. (UK Und., also twelve) one shilling (5p) [the twelve pennies it represented, use after 1730s mainly Aus.].

c.1698		B.E. Dict. Canting Crew n.p.: Twelver a shilling.
1725		New Canting Dict. [as cit. c.1698].
1733		in J. Malcolm Anecdotes of Manners and Customs (1808) 89: The particular saucy impudent behaviour of the coachman in demanding the other twelver or tester above their fare, has been the occasion of innumerable quarrels, fighting, and abuses.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
a.1790		H.T. Potter New Dict. Cant (1795).
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum.
1821		‘An Amateur’ Real Life in London I 559: Many a twelver† does he get by buying up broken images of persons who sell them by wholesale, and he of course gets them for little or nothing. [† Twelver — A shilling].
1839		H. Brandon Dict. of the Flash or Cant Lang. 166/1: Twelve, Twelver – a shilling.
1848		Flash Dict. in Sinks of London Laid Open.
1852		Kendal Mercury 17 Apr. 6/1: Three twelves and a tanner (3s. 6d.).
1852		Kendal Mercury 17 Apr. 6/1: Arter I’d been there three hours all I got vas a twelver (shilling).
1858		A. Mayhew Paved with Gold 267: He had been out all day on the ‘monkry,’ and had only taken three ‘twelvers’ and a ‘grunter.’.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn).
1864, 1867, 1870		Hotten Sl. Dict.
1881		Morn. Bulletin (Rockhampton, Qld) 18 July 2/6: For a shilling there are many names but nearly all slang. [...] ‘Breaky-leg,’ ‘brongs,’ ‘bobs,’ ‘bordes,’ ‘drawers,’ ‘gens’, ‘hogs,’ levys,’ ‘pegs,’ ‘stags,’ ‘Shigs,’ ‘twelvers’ and ‘teviss’s’ .
1895		Crowe Aus. Sl. Dict. 90: Twelver, a shilling.
1901		Argus (Melbourne) 20 Sept. 6/4: A shilling is generally a deaner or a twelver.
1925		(ref. to 1850s) Western Mail (Perth) 28 May 21/1: [from Daily Mail, London]At the time of the Crimean War bob was only one of a number of terms [for a shilling] such as twelver and breaky-leg, gen and teviss, stag, deaner, hog and levy.

2. (Aus./UK Und.) a twelve-month sentence.

1858		Bell’s Life in Sydney 27 Nov. 3/2: Polly Murphy was sent to jail for a twelver.
1871		Manchester Eve. News 6 Dec. 4/2: When it was seen that his wife was in a dangerous state, the prisoner said, with infamous indifference, ‘Let the — cat do a stiff un. I can do a “twelver” for her’.
1885		Bulletin (Sydney) 11 July 20/1: They thought, no doubt, that the man [...] walked about the town singing softly to himself, ‘Two floggings and a twelver – oh, that’s the game for me.’.
1894		Hull Dly Mail 17 Aug. 4/1: It will be a sixer or a twelver for a job like this.
1909		Derby Dly Teleg. 25 May 2/6: He [...] said he would ‘do a twelver for him in nine months’.