Well, Arly, if you call it a "showtune," it has the implication that it was written for a Broadway musical. If you say it was written for the Yiddish theater, it doesn't sound so crassly commercial.

There are three Mlotek Yiddish songbooks, and all three are true pearls. The first, Mir Trogn a Gesang, was first published in 1972 and reissued in March, 2000 (it was unavailable for quite some time). Pearls of Yiddish Song was published in 1988. Songs of Generations: New Pearls of Yiddish Song was published sometime after 1994, but I can't find a copyright date in the book. You can contact the publisher, Workmen's Circle, at http://www.circle.org/. All three books are now available at http://www.jewishmusic.com, which has a complete list of all the songs in all three books.
-Joe Offer-