Definition - A comically incorrect word that is mistakenly used in place of another similar word.

Example -
He committed a carnival sin.

Etymology -
The word derives from the name Mrs. Malaprop, a character in Sheridan's play The Rivals (1775), who ridiculously misused large words. Sheridan derived her name from the French mal à propos, which literally means "badly for the purpose" (from French mal, bad + proposer, propose).

Oxford English Dictionary -
Its first citation is from 1849:
"A malapropism which rumour had not failed to repeat."
(C. Bronte, Shirley II. vi. 145)

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