When you put your dick between a girls butt cheeks and she wanks your cock using her butt.
That slut jessica gave me a bumwank last night it was good
by Jack_Bauer January 21, 2006
like a tit wank but with your arse
kristen didn't want full anal so offered a bum wank instead
by watermelonclitlicker May 31, 2010
Absolute spanner. A term used in frustration towards someone who has pissed you off.
"Oi, bumwank, what did you do that for?"
by Fairly Talented Thespian January 30, 2008