bumbosity, n. — Green’s Dictionary of Slang

bumbosity n.

also bombosity

[artificially extended bum n.¹ (1)]

(US) the buttocks.

1932		J.L. Kuethe ‘Johns Hopkins Jargon’ in AS VII:5 329: bombosity—the buttocks.
1950		WELS n.p.: (Joking words for the part of the body that you sit on) Bumbosity [...] Bombosity [DARE].
1960, 1975		Wentworth & Flexner DAS.
2000		Sex-Lexis 🌐 bombing the german helmet; bombosities, bombosity.
2004		(ref. to 1930s) www.wordwizard.com 🌐 The very eyedocity, you shock my modesty, / If I didn’t have my kid gloves on I’d spank your bombosity!