Green’s Dictionary of Slang

dummy n.1

[SE dumb; note Egan, Life in London (1821): ‘A cant phrase for a stupid fellow; a man who has not a word to say for himself. The family of the dummies is very numerous’]

1. [late 16C+] (also dumbie, dumby) a dumb (i.e. mute) person.

2. attrib. use of sense 1.

3. [19C+] a fool, an idiot.

4. [mid-19C] a dumb animal.

5. [mid-19C; 1910s+] a deaf mute, or a tramp or beggar who pretends to be deaf and dumb.

6. [1920s] (US Und.) a detective.

7. [1930s] (UK Und.) one who poses (or is unwittingly exploited) as the law-abiding owner of an establishment, e.g. a nightclub, to shield the criminal who is the actual owner.

8. [1930s+] (also dummie) a retarded person.

9. [1950s+] (N.Z. Und.) solitary confinement; the solitary confinement/punishment cell in a prison (the inmate is forced to be silent).

In compounds

dummy dodge (n.)

[1910s] (US tramp) posing as a deaf mute to elicit alms.

dummy dust (n.) [a drug that appeals to or creates a dummy (i.e. sense 2 above) + dust n. (5e)]

[1970s+] (drugs) phencyclidine.

In phrases

catch a dummy (v.)

[1970s] (US prison) to refuse to talk.

dummy out (v.)

[1970s] (drugs) to lose awareness and coordination through drug use.

go on the dummy (v.)

[1930s–70s] (US) to stop talking, to be quiet.