Douglas Harper's Etymology Dictionary
folk-etymology
1890; see folk (n.) + etymology.\n\nBy Folk-etymology is meant the influence exercised upon words, both as to their form and meaning, by the popular use and misuse of them. In a special sense, it is intended to denote the corruption which words undergo, owing either to false ideas about their derivation, or to a mistaken analogy with other words to which they are supposed to be related.
[The Rev. A. Smythe Palmer, "Folk-Etymology," 1890]
Usage examples of "folk-etymology".
Cylart from Carnarvon was due to the etymologising fancy of some English-speaking Welshman who interpreted the name as Killhart, so that the simpler legend would be only a folk-etymology.