Keister
wiktionary
Origin uncertain. Originally attested as a criminal cant word for "burglar's tool-box" in 1881. In the 20th century a clutch of criminal slang meanings are mentioned, including "safe, strongbox". "Tripe and keister" had been the phrase for a conman's or a pitchman's display case on a tripod. A likely origin is the word Kiste, which means a box or case, in both German and Yiddish.
etymonline
keister (n.)
"buttocks," 1931, perhaps transferred from the same word in an underworld meaning "safe, strongbox" (1914), earlier "a burglar's toolkit that can be locked" (1881); probably from British dialect kist (northern form of chest (n.)) or its German cognate Kiste "chest, box." The connection of the word to the body part might be via the pickpocket slang sense of "rear trouser pocket" (1930s).
