I just stumbled upon a truly remarkable etymology. I’ve finally gotten around to reading Pushkin’s Капитанская дочка [Kapitanskaya dochka, “The Captain’s Daughter”], one of those all-time classics I should have read several decades ago, and I’ve reached the brigand song “Не шуми, мати зеленая дубровушка” in Chapter VIII (and if anyone can point me to an audio file of this or a similar choral song so I can get an idea of what it sounds like, I’ll be deeply grateful). When the song’s protagonist proudly answers back to the tsar that his comrades are the dark night and his knife, horse, and bow, the tsar begins his response Исполать тебе, детинушка крестьянский сын! ‘Hail to thee, young fellow, son of the peasantry!’ I was curious about the word Исполать [ispolát’] ‘hail!’; I’d never seen a more Slavic-looking word, but the derivation wasn’t immediately obvious. So I went to my trusty Vasmer, and discovered it was a 16th-century borrowing from Greek εις πολλά έτη [is pola eti] ‘[may you live] for many years,’ which in rapid speech would become /ispoláti/! I’ll bet that provides fertile ground for folk etymology.
(Oh, in case you were wondering, the tsar in the song promises the brave young brigand a fine home… in the form of a gallows.)