Green’s Dictionary of Slang

1. (also bot-bot) the buttocks.

1922		Joyce Ulysses 505: You will dance attendance or I’ll lecture you on your misdeeds, Miss Ruby, and spank your bare bot right well, miss, with the hairbrush.
1943		R. Llewellyn None But the Lonely Heart 115: He [...] give Ma Sitram a fine old slap across the bott. [Ibid.] 184: Reg [...] gives the bride a smack across the bot.
1979		‘Abdul Abul Bul Amir’ in Bold (1979) 3: He felt something hot whistle straight up his bot.
1982		P. Bailey Eng. Madam 121: On their bot-bots, Nanny.
2003		McGill Reed Dict. of N.Z. Sl.

2. an act of homosexual anal intercourse.

1997

Roger’s Profanisaurus in Viz 87 Dec. n.p.: bott v. A sex act performed by botters (qv).