folk etymology
Definition - Another name for popular etymology, a word-creation process where an existing word is modified because of a mistaken assumption about its composition or meaning. Usually the new word makes the other word's parts more meaningful.

Example -

(1) The Old English word agnail — which denoted a "swelling around the nail" — evolved into hangnail, a word that seems to better describe the phenomenon.

(2) Similarly, the word shamefaced was derived from shamfast, bound by shame, and cutlet was derived from French côtelette, little rib.

Etymology -
The term was coined as a loan translation of the German Volksetymologie.

Oxford English Dictionary -
Its first citation is from 1883:
"It does not mend the matter, if, when we have no better argument, we call it *folk-etymology."
(G. Stephens and S. Bugge's Studies on Northern Mythology, p 28)

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