Definition: the buttocks
When one is engaged in dinner party conversation, one occasionally hears another guest make some assertion about the English language, such as “there is no word which rhymes with purple.” The polite response to such a statement is to nod your head and exclaim something along the lines of “What an interesting and well-learned fellow you are! Your parents must be quite proud.” If you are not a polite person, you might instead point out that there are not one, but two words in the Scottish dialect of English which rhyme with purple: curple (which may refer to “a leather loop passing under a horse’s tail and buckled to the saddle” or to the buttocks of a horse or other creature) and hirple (“to walk with a limp”).
I’m afraid that John Durie has cracked his curple, at least his mouth is closed.
—David Hume (letter to James Carmichael, 15 Mar. 1585), in The Miscellany of the Wodrow Society, 1844