Bridegrooms, Bonfires, and Woodchucks: Folk Etymologies in English. From that link:
- The textbook examples for English are sparrowgrass for asparagus, and bridegroom, which should have been bridegoom. (The word gome for “man” became extinct, so people grabbed the nearest similar word. Now that the noun groom for “horse attendant” has also become extinct, people use groom to mean bridegroom.)
- Apparently cockroach is a folk etymology mangling of cucaracha, and Algonquin otchek became woodchuck.
- A bonfire was originally bonefire; people assumed the bon- is French.
- The change of femelle to female in English was a folk etymology linking it to male.
An example I discovered just this year, because of Quora, is the Greek for toyboy or twink, teknó. It looks like a mis-stressed version of the Ancient Greek téknon “child”, the word with which priests address their parishioners. (Insert your own joke here.)
In fact, it’s from the Romany tiknó, “small (child)”. Kaliarda, the cant of Greek street queens in the 60s, used Romany for its base vocabulary, just as its counterpart Polari for English used Italian. Someone along the line noticed the similarity of tiknó to téknon, and switched the vowel accordingly. (Amusingly, someone also noticed it in 1800: Etymologicon magnum, or Universal etymological dictionary, on a new plan [By W. Whiter].)
… Unless Romany tiknó is derived from téknon itself, of course. But I’m reasonably sure it isn’t: Scandoromani derives it from Sanskrit tīkṣṇa “sharp”.