Green’s Dictionary of Slang

mule n.

1. [mid-17C; 19C+] a fool, a stubborn person [on model of ass n.].

2. [20C+] any small motor-powered vehicle.

3. as a form of alcohol [the alcohol ‘kicks like a mule’].

(a) [1910s+] (US) homemade bourbon made from grain alcohol.

(b) [1950s] (US drugs) marijuana soaked in bourbon.

4. in drug uses.

(a) [1920s+] (drugs) a carrier of drugs, typically across international borders, and in many cases an otherwise ‘innocent’ person who has no other contact with the drugs trade.

(b) [1930s+] a drug runner, operating within a given city or prison; on a local scale, the runner who brings supplies from an adjacent hiding place to a street dealer as demand requires.

(c) [1960s+] (US prison, also packhorse) a smuggler, usu. a visitor or prison warder.

(d) [1990s+] any form of carrier, e.g. of weapons for a gang.

5. [1920s+] (US) the penis [earlier cits. are doubles entendres].

6. [1940s+] as a derog. description.

(a) an unattractive woman.

(b) (US campus) an unattractive man.

(c) an impotent man.

(d) (W.I.) an infertile woman, who therefore suffers from mule-belly.

7. [1960s] (US) vodka.

In phrases

corn mule (n.)

[1920s–60s] (US) illicitly distilled corn whisky.

gray mule (n.)

[1900s–10s] (US) corn whisky or gin.

lope the mule (v.) (also lope, lope one’s mule, ...donkey, ...pony)

[1950s+] (US) to masturbate.

ride the mule (v.)

[1990s+] to have sexual intercourse.

SE in slang uses

In compounds

mule breakfast (n.)

[1920s–40s] (US) a straw hat.

muledick (v.)

[1970s] (US) of a man, to copulate aggressively, violently.

mule-mouth (n.)

[1970s+] (US black) one who works regularly as a police informer.

mule whacker (n.) (also mule-puncher) [whack v.1 (1)]

[late 19C–1920s] (US) a mule-driver.

In phrases

here’s your mule

[mid-19C] (US) a nonsensical phr. used by troops during the US Civil War.

In exclamations

mule shit! [var. on bullshit n.]

[1920s+] (US) a mild oath, used to express disbelief or surprise.