Curious about my own question, when things slowed down this evening, I did a
quick search in the MT's World CD and found the word used in the following
works: PW, GE, TA, IA, RI, LM, TS, HF, TSA, TSD, AC, Autobiog., True Story,
Johnny Greer, Curing a Cold, Curious Exp. and two letters (1898 to Howells,
1893 to Fred Hall).  Although not found in my CD search I'd add to this list
Capt Stormfield, King Leopold, and Letters from the Earth, plus the ca.
1900-1905 letter, at least another 2-3 letters, the notebooks, and other
short sketches or newspaper pieces.

I didn't spend much time checking the context of each literary use, but each
one I did look up was spoken by a character, or was a quote of somebody
else's speech, rather than Twain himself as narrator.

Tracking down his specific uses in his letters and "non-literary" contexts
would take a good deal more time and effort, and I have too many irons in
the fire at the moment, some of them Twainian, but I hope somebody follows
up in this direction and presents a paper on it at the next Elmira
Conference where they'll find me sitting down front to hear it.

Kevin Mac Donnell
Austin TX