A malapropism is an absurd misuse of a word, usually confusing it with another that sounds similar. It comes from the word malaprop, itself from malapropos: out of place; inappropriate. The term probably came into vogue in the 1800’s.  

Malapropos is itself from the French phrase mal àpropos: mal=bad; à=to; propos=purpose, subject (thus, also, àpropos). It means “inappropriate”.

Mrs Malaprop, a character in Sheridan’s successful play “The Rivals” (1775), has a deliciously approximate grasp of the language:

• “She’s as headstrong as an allegory on the banks of the Nile”
• “He is the very pineapple of politeness”
• “If I reprehend any thing in this world, it is the use of my oracular tongue, and a nice derangement of epitaphs!”

Mrs Malaprop gave her name to the phrase, and, arguably, paved the way for Dubya.