Knee-slapper is an idiom that has been in use for less than 100 years. We will examine the meaning of the common idiom knee-slapper, where it came from, and some examples of its idiomatic usage in sentences.
A knee-slapper is an uproariously funny joke; the idea is that the joke is so funny, one collapses into laughter when one hears it, slapping one’s knee. Knee-slapper is a hyphenated compound word, which is a word derived from two or more separate words used together with a hyphen to create another word. Compound words are new words that have a different meaning from the definitions of the original words. The expression knee-slapper is American; it came into use in the mid-twentieth century.
Examples
Not exactly a knee-slapper in a different context, but this quote drew laughter from audience when DeVillers refused to bite on a bit of gamesmanship from a reporter trying to get him to break prosecutorial protocol. (Columbus Monthly)
Not to be outdone, Francois Legault’s government last week came up with a knee-slapper of a plan to give a subsidy to every Quebecer with a driver’s licence. (Montreal Gazette)
And repeating a real knee-slapper ranks high among life’s basic joys. (Reuters)