Green’s Dictionary of Slang

behind n.

1. [mid-16C+] the buttocks, the posterior.

2. [late 19C+] used anthropomorphically, the back of an object, e.g. a car, a bus.

In derivatives

behindativeness (n.) [SE behind/sense 2 above + sfx -ative, tending to point out]

[late 19C] a large dress-pannier, fashionably affixed to a lady’s dress c.1888.

In compounds

In phrases

behind the behind (n.) [SE behind + sense 1 above ]

[1930s] sodomy.

not know where one’s behind hangs (v.)

[20C+] to be arrogant or to show complete indecision or bewilderment.

warm someone’s behind (v.)

[1970s–80s] (US black) to hit or slap someone on the buttocks.