Definition: an act of foolishness orstupidity
Bêtise came to English from the French wordbête, which has the meaning in that language of "idiot," or, moreliterally, "beast" (the literal meaning of bête is the one found inthe term bête noire). In addition to an act of stupidity, bêtise may refer to stupidityor ignorance in general.
"I assure you," said she "Iwas only tormenting you a little, and you must own you deserve that; but youcan't suppose I meant half what I said; that is a bêtise I can't conceive youguilty of.”
— Susan Ferrier, Marriage 1818