Green’s Dictionary of Slang

bamsie n.

also bamsee
[bum n.1 (1)]

(W.I.) the buttocks, the posterior.

T.G. Marshall et al. Folk Songs of Barbados 98/1: The young lady walks making her ‘bamsee’ — hips — wriggle from side to side.
[UK]R. Antoni Grandmother’s Erotic Folktales 37: Layers of white frills rippling down she long neck, down over she ripe tot-tots, and down around she smooth, shapely bamsee. [Ibid.] 78: But the hips could still wind a little bit, and the bamsee could still shake.
J. Lyons Voices from a Silk-cotton Tree 57: Dresses slipped off her shoulders, often got caught in the fat-folds of her waist, her bamsie-crease.
[UK]R. Antoni Carnival 155: Jennifer was back-backing her half-exposed bamsee against my crotch.

In compounds