Green’s Dictionary of Slang

bot n.3

also bott
[abbr. SE bottom]

1. (also bot-bot) the buttocks.

[Ire]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.
[UK]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.
[UK] ‘Abdul Abul Bul Amir’ in Bold (1979) 3: He felt something hot whistle straight up his bot.
[UK]P. Bailey Eng. Madam 121: On their bot-bots, Nanny.
[Aus]Courier-Mail (Brisbane) 7 July 7/6: Johnny Depp fans will have to learn to live with the devastating news that, when he bares his bot-bot in his latest film [...] the cheeks that appear on screen will not be the dinkum.
[NZ] McGill Reed Dict. of N.Z. Sl.

2. an act of homosexual anal intercourse.

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

3. (Aus. gay) the passive member of a homosexual S&M duo, i.e. bottom n.3 (2)

[Aus]Capital Q (Sydney) 12 Mar. 38/5: [personal advert] Horny top. Needs well behaved bot to service [Simes:DLSS].