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).
[1910s] (US tramp) posing as a deaf mute to elicit alms.
[1970s+] (drugs) phencyclidine.
[1970s] (US prison) to refuse to talk.
[1970s] (drugs) to lose awareness and coordination through drug use.
[1930s–70s] (US) to stop talking, to be quiet.