KEYSTER

To vaudevillians this word meant suitcase, but the meaning changed to mean one's posterior. I can see why and how it changed, but have never been able to confirm it. [Didn't the vaudevillians spell it keester or keister?] My friend was 90yrs. old and corrected me on its use and meaning. Example: He fell on his keyster. He sat on his keyster.