Malapropism
Etymology
From Mrs. Malaprop, a character in Sheridan’s 1775 comedy The Rivals who constantly mangles her vocabulary. Sheridan built her name from the French phrase mal à propos, "inappropriately, ill-suited." So the word for the blunder is named after the fictional woman famous for committing it.
noun · /MAL-uh-prop-iz-um/
The unintentional, comic use of a word in place of a similar-sounding one, with absurd effect.
What it names
The accidental laugh of "he is the very pineapple of politeness" — reaching for a word and grabbing its near-twin, exposing a gap between what someone meant and what they said.
Example
The best malapropism in the meeting was "let’s not jump to seclusions," and no one had the heart to correct it.
Related idea
Spoonerism also garbles speech, but by swapping sounds between words rather than substituting a whole wrong word for a right one.