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Wiktionary
folk etymology

n. 1 A misunderstanding of the etymology of a word; a false etymology that incorrectly explains the origin of a word. 2 A modification of a word or its spelling resulting from such a misunderstanding, as with ''island'', ''belfry'', and ''hangnail''.

WordNet
folk etymology

n. a popular but erroneous etymology

Wikipedia
Folk etymology

Folk etymology, pseudo-etymology, or reanalysis is change in a word or phrase over time resulting from the replacement of an unfamiliar form by a more familiar one. Unanalyzable borrowings from foreign languages, like asparagus, or old compounds such as samblind which have lost their iconic motivation (since one or more of the morphemes making them up, like sam-, which meant "semi-", has become obscure) are reanalyzed in a more or less semantically plausible way, yielding, in these examples, sparrow grass and sandblind.

The term folk etymology, a loan translation from the 19th-century academic German Volksetymologie, is a technical one in philology and historical linguistics, referring to the change of form in the word itself, not to any actual explicit popular analysis.