In linguistics, an eggcorn is an idiosyncratic substitution of a word or phrase for a word or words that sound similar or identical in the speaker's dialect (sometimes called oronyms). The new phrase introduces a meaning that is different from the original but plausible in the same context, such as "old-timers' disease" for "Alzheimer's disease". An eggcorn can be described as an intra-lingual phono-semantic matching, a matching in which the intended word and substitute are from the same language.
The term eggcorn was coined by professor of linguistics Geoffrey Pullum in September 2003 in response to an article by Mark Liberman on the website Language Log, a blog for linguists. Liberman discussed the case of a woman who substitutes the phrase egg corn for the word acorn, and he argued that the precise phenomenon lacked a name. Pullum suggested using eggcorn itself as a label.
An eggcorn differs from a malapropism, the latter being a substitution that creates a nonsensical phrase. Classical malapropisms generally derive their comic effect from the fault of the user, while eggcorns are substitutions that exhibit creativity, logic or ignorance. Eggcorns often involve replacing an unfamiliar, archaic, or obscure word with a more common or modern word ("baited breath" for "bated breath").
The phenomenon is similar to the form of wordplay known as the pun except that, by definition, the speaker or writer intends the pun to have some humorous effect on the recipient, whereas one who speaks or writes an eggcorn is often unaware.