Green’s Dictionary of Slang

1. a miniskirt.

1967		Punch 27 Dec. 986: The rag trade’s mini maxi race is hotting up.
1970		T. Southern Blue Movie (1974) 26: Leaning over in such a way that her extremely brief mini revealed the back of bare brown legs and a precious, perfectly rounded derrière.
1972		C. Bukowski Erections, Ejaculations etc. 142: An eighteen-year-old cunt with a mini up to her hips, high heels and long stockings.
1980		M. Thelwell Harder They Come 292: He was [...] angry with Elsa for not coming, for refusing even to try on the mini that he had so carefully selected.
1982		Dly Record (Morristown, NJ) 28 Oct. 25/3: You’ll look bitchen in your mini.
1985		B. Humphries Traveller’s Tool 7: Looking up the leather mini of the spunky little hornbag.
2000		Guardian G2 1 Feb. 6: A group of women in identical minis, red lipstick and slicked-back hair.

2. (N.Z. prison) on who has a rectum considered too small to hold much contraband; the rectum itself.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 117/1: Mini, the n. 1 a small rectum able to conceal only a meagre amount of contraband 2 an inmate with a small rectum.