keister

• n. 手提皮箱；屁股；小皮包

可能来自chest拼写变体，用于俚语义屁股。

1. the fleshy part of the human body that you sit on;

"he deserves a good kick in the butt"

"are you going to sit on your fanny and do nothing?"

keister (n.)

"buttocks," 1931, perhaps transferred from underworld meaning "safe, strongbox" (1914), earlier "a burglar's toolkit that can be locked" (1881); probably from British dialect kist (northern form of chest) or its German cognate Kiste "chest, box." The connection may be via pickpocket slang sense of "rear trouser pocket" (1930s).