Folly
Middle English: from Old French folie ‘madness’, in modern French also ‘delight, favourite dwelling’ (compare with folly (sense 2)), from fol ‘fool, foolish’.
wiktionary
From Old French folie(“madness”), from the adjective fol(“mad, insane”).
etymonline
folly (n.)
early 13c., "mental weakness; foolish behavior or character; unwise conduct" (in Middle English including wickedness, lewdness, madness), from Old French folie "folly, madness, stupidity" (12c.), from fol (see fool (n.)). From c. 1300 as "an example of foolishness;" sense of "costly structure considered to have shown folly in the builder" is attested from 1650s. But used much earlier, since Middle English, in place names, especially country estates, probably as a form of Old French folie in its meaning "delight." Related: Follies.
