/kee"steuhr/ , n. Slang.
the buttocks; rump.
Also, keester .
[ 1880-85; earlier, as underworld argot, handbag, suitcase, safe; of obscure orig., but words meaning "chest, box" are frequently adduced as sources, e.g., KIST 1 , G Kiste, Yiddish kestl, etc. ]