etymythology
A false etymology that has become widely disseminated and thus is commonly accepted as true; a folk etymology.
The basic element which transforms names and placenames into narratives or narrative details is the pun. I call this process etymythology. and I show how James Joyce's knowledge of Irish onomastic and toponomastic tales, and his interest in the process which created them, was bolstered by his early study of the developing science of etymology, […] to the point where etymythology as poetics became one of Joyce's own methods of composition, an element of his own poetics.
Where it comes from
Blend of etymology + mythology. Though the term is modernly believed to be coined by linguist Laurence R. Horn in 2004, there are linguistic uses that go back to 1969 by Sean Valentine Golden.
Adapted from the Wiktionary entry etymythology (CC BY-SA 4.0).