The term folk etymology is a loan translation from German Volksetymologie, coined by Ernst Förstemann in 1852. Folk etymology is a productive process in historical linguistics, language change, and social interaction. Reanalysis of a word's history or original form can affect its spelling, pronunciation, or meaning. This is frequently seen in relation to loanwords or words that have become archaic or obsolete.
Examples of words created or changed through folk etymology include the English dialectal form sparrowgrass, originally from Greek ἀσπάραγος ("asparagus") remade by analogy to the more familiar words sparrow and grass, or the word burger, originally from Hamburg + -er ("thing connected with"), but understood as ham + burger.
The technical term "folk etymology" refers to a change in the form of a word caused by erroneous popular beliefs about its etymology. The English word is a translation of the German term Volksetymologie, coined by Ernst Förstemann. Förstemann noted that in addition to scientific etymology based on careful study in philology, there exist scholarly but often unsystematic accounts, as well as popular accounts for the history of linguistic forms. Until academic linguists developed comparative philology and described the laws underlying sound changes, the derivation of words was a matter mostly of guess-work. Speculation about the original form of words in turn feeds back into the development of the word and thus becomes a part of a new etymology.
Believing a word to have a certain origin, people begin to pronounce, spell, or otherwise use the word in a manner appropriate to that perceived origin. This popular etymologizing has had a powerful influence on the forms which words take. Examples in English include crayfish or crawfish, which are not historically related to fish but come from Middle English crevis, cognate with French écrevisse. Likewise chaise lounge, from the original French chaise longue ("long chair"), has come to be associated with the word lounge.
Rebracketing is a process of language change in which parts of a word that appear to be meaningful (such as *ham in hamburger) are mistaken as elements of the word's etymology (in this case, the word ham). Rebracketing functions by reanalyzing the constituent parts of a word. For example, the Old French word orenge ("orange tree") comes from Arabic النرنج an nāranj ("the orange tree"), with the initial n of nāranj understood as part of the article.
In back-formation a new word is created, often by removing elements thought to be affixes. For example, Italian pronuncia ("pronunciation; accent") is derived from the verb pronunciare ("to pronounce; to utter") and English edit derives from editor. Some cases of back-formation are based on folk etymology.
In linguistic change caused by folk etymology, the form of a word changes so that it better matches its popular rationalisation. Typically this happens either to unanalyzable foreign words or to compounds where the word underlying one part of the compound becomes obsolete.