Usually spelled keister (there are many alternate spellings), the original meaning of this American slang word is a satchel or suitcase. A later, and now more common sense, is that of a person’s rump or buttocks.
Dating in English to 1882, the term is from the German Kiste meaning box or case—the slang sense of rump also exists in the German. From George Wilbur Peck’s Peck’s Sunshine of that year:
The boy took the knight’s keister and went to the elevator.
A year earlier than this quote, Alfred Trumble’s The Man Traps of New York uses the word as a nickname, probably a reference to a man known for carrying a case:
Prominent among the small army of confidence operators in this city are “Grand Central Pete,"..."Boston Charlie,"..."Keister Bob,” “The Kid,” “Hungry Joe.”
Presumably, the sense of the buttocks developed because a traveling case was something you could sit upon. The earliest known citation is from an American Speech article on convict’s slang from 1931:
keister, n. A satchel; also what one sits on.
Copyright 1997-2013, by David Wilton