Green’s Dictionary of Slang

1. a fit, whether physical or emotional, but usu. faked; usu. as chuck a dummy under chuck v.²

1880		implied in chuck a dummy under chuck v.2
2004		S. James in Guardian 6 July 28/4: His intemperate tirade [...] after being adjudged leg-before to Lance Klusener, was a remarkable piece of sustained dummy-throwing.

2. (UK Und.) a mannequin, garbed in a coat hung with bells, used to train pickpockets.

1925

N. Lucas Autobiog. of a Thief 107: The ‘dummy’ [is] a sack filled with straw and clothed in a coat. The ‘dummy’ is garnished with sensitive little bells which tinkle on the slightest jar.

3. (US Und.) a roll of counterfeit money.

1935		A.J. Pollock Und. Speaks 35/1: Dummy, twenty dollar gold pieces in stacks of twenty five placed in a rack (only 2 or 3 genuine gold pieces on top – the remainder being gold paper) to make it appear that the gambling house has a large bank roll.
1939		Howsley Argot: Dict. of Und. Sl. 17: dummy – [...] a counterfeit, copy.
[1949		Monteleone Criminal Sl. (rev. edn) 76: dummy [...] false or worthless merchandise].
1979		‘Iceberg Slim’ Airtight Willie and Me 15: He pressed the dummy into her hands.

4. (drugs) poor-quality or fake drugs.

[1949		Monteleone Criminal Sl. (rev. edn) 76: dummy [...] worthless merchandise].
1966		J. Mills Panic in Needle Park (1971) 147: They’ll even forget it if you deal them a dummy. But rat. No, sir. That is something else. That is the worst.
1971		E.E. Landy Underground Dict. (1972).
1981		D.E. Miller Bk of Jargon 341: dummy: Fake heroin.
1990		(con. 1930s–60s) H. Huncke Guilty of Everything (1998) 276: There were guys making hand over fist selling dummies.
1997		L. Pettiway Workin’ It 132: I cop right there at that building [...] Never been given dummies.
2003		G. Pelecanos Soul Circus 162: I’ll give what I got for some dummies I can sell out there on the strip. I can make a quick rack of money like that.

5. (N.Z. prison) a test package, with no actual contraband, used to test of potential smuggling route.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 62/2: dummy n. a false package containing non-incriminating material sent into or out of the prison through a certain proposed channel in order to test the suitability of that channel for the smuggling of real contraband.