Folk etymology (or popular etymology) is a linguistic term for the modification of a word or phrase based on an analogy or an erroneous etymology which is popularly believed to be true.
In popular usage, the term has also come to mean an "explanation" of the meaning of a word based on its superficial similarity to other words and not on its morphology, documented history or scientifically reconstructible past forms. An example is this passage, collected via Internet, from a New Jersey excursion to find evidence of Bigfoot: "It took about an hour and a half to reach the mountain. It is called Apshawa Mountain (not sure, but 'Apshawa' sounds like it may mean 'ape' or something to that effect in Native American)." Faulty assumptions in this casual attempt at etymology include that 'Native American' is a single language; that Native American languages would have a term for the African and Asian primates called 'apes'; and that a Native American word for 'ape' would sound like the English word, 'ape.' In linguistics such an etymology is a fake etymology.
'Folk etymology,' in the linguistic sense, is the process by which a word or phrase changes because of a popularly-held fake etymology, or misunderstanding of the history of a word or phrase.
Instances of folk etymology
In folk etymology, the form of a word changes so that it better matches its popular rationalisation. For example, Old English sam-blind 'semi-blind' or 'half-blind' became sand-blind (as if 'blinded by the sand') when people were no longer able to make sense of the element sam 'half', and Old English bryd-guma 'bride-man' became bridegroom after the loss of the Old English word guma 'man' (compare French 'homme') rendered the compound semantically obscure. The silent s in island is also a result of folk etymology. The word, which derives from an Old English compound of ig 'water' (surprisingly, cognate to Latin aqua) with land, was erroneously believed to be related to isle, which has a similar meaning but derives from Latin insula 'island.' More recent examples are French (e)crevisse (likely from Germanic krebiz) which became English cray-fish or asparagus which became sparrow-grass. Similarly, cater-corner became kitty-corner when the original meaning of cater, "four", had become obsolete.
In one example from non-sexist language, feigned folk etymology was the source of neologisms like herstory to replace history. To make it clear, the idea is that the story of mankind is his story but also her story. In actuality, the word history is etymologically unrelated to the possessive pronoun his; it is from the Greek word historia, meaning 'learning or knowing by inquiry'.
In heraldry, a rebus coat-of-arms may reinforce a folk etymology for a placename.
- Adrian Room, Dictionary of True Etymologies, 1986, Routledge & Kegan Paul