Green’s Dictionary of Slang

1. to prepare, to get ready.

1850

Manchester Spy (NH) 5 Oct. n.p.: A chamber of the hotel, where we had something Cooper-ed up in tall shape.

2. (UK Und.) to forge, to counterfeit; thus cooper, a forger.

1858		A. Mayhew Paved with Gold 269: His false petitions were highly esteemed, and he enjoyed the reputation of being a first-rate fist at ‘screeving a fakement,’ though, owing to his forged signatures having been too often detected, he was declared to be ‘a duffer at coopering a monekur’.
1864, 1867, 1870		Hotten Sl. Dict.
1869		Australiasian (Melbourne) 17 July 8/5: To forge is to ‘cooper,’ cooper meaning to destroy, and a cooper's mark is [a] triangle, which signifies that ‘business’ has been overdone.
1882		Sydney Sl. Dict. (2 edn) 2: Cooper - To spoil or destroy. To forge or imitate in writing. ‘Cooper a monniker,’ to forge a signature.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1895		Crowe Aus. Sl. Dict. 19: Cooper, to forge, or imitate in writing.
1935		A.J. Pollock Und. Speaks 25/2: Cooper, a forger.

3. to spoil, to ruin.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1874		‘Old Calabar’ Won in a Canter II 287: [of interfering with a racehorse] ‘[T]he horses are not likely to win and we can gammon him tbat we coopered them’.
1880		Leicester Chron. 4 Sept. 9/6: His companion was [...] so jolly in countenance that he ‘coopered’ their ‘griddling’ [...] no one gave them anything.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1891		F.W. Carew Autobiog. of a Gipsey 434: There’s such a thing as perfeshional pride, and if we sh’d ’appen to get rung or pinched, I sh’ldn’t like ter ’ave it brought agen me that I’d coopered the job.
1907		D. Stewart Vultures of the City in Illus. Police News 12 Jan. 12/3: ‘He’ll get this house coopered (spoilt) before he has done playing his infernal hankey-pankey’.
1913		Chelmsford Chron. 21 Feb. 7/4: The vagrants themselves were well acquainted with the system [...] when they heard that essex was going to adopt the system they would say another good county was ‘coopered’ .

4. to consume.

1890

Sporting Times 26 Apr. 3/3: The valiant voyager wound up his old Dutch, with his old D., I should say, who proving a tougher morsel than the wolves could cooper in ten minutes for refreshments, he was enabled to get such a start that they were powerless to again overtake him.

5. see copper v.² (1)