Hints (highlight to view):
OK, OK, I don't really expect you to know that. But you can deduce it from these clues (which should also disambiguate it for the few of you who know one of those languages well enough to know that they have multiple words for joke):
The answer I was looking for is Witz. Jason and Leo S. pointed out that my "three Proofniks" clue could have been "four Proofniks", if the vitz spelling counts. (As it should! The actual spelling in Yiddish is וויץ, and "vitz" is the romanization that best represents how it is pronounced.)
Aptly, yesterday's solvers included Jason, Zoe, and Zachary. I didn't hear from Alex, hopefully because he was too busy celebrating his birthday. Congrats also to Leo S., Jessica, Anna K., Carl, Harper, Maddy, Peter M., Josh M., Charlie, and Mr. Gregg!