early 13c., “silly, stupid, or ignorant person,” from Old French fol “madman, insane person; idiot; rogue; jester,” also “blacksmith’s bellows,” also an adjective meaning “mad, insane” (12c., Modern French fou), from Medieval Latin follus (adj.) “foolish,” from Latin follis “bellows, leather bag” (see follicle).
The sense evolution probably is from Vulgar Latin use of follis in a sense of “windbag, empty-headed person.” Compare also Sanskrit vatula- “insane,” literally “windy, inflated with wind.” Some sources suggest evolution from Latin folles “puffed cheeks” (of a buffoon), a secondary sense from plural of follis. One makes the “idiot” sense original, the other the “jester” sense.
The word has in mod.Eng. a much stronger sense than it had at an earlier period; it has now an implication of insulting contempt which does not in the same degree belong to any of its synonyms, or to the derivative foolish. [OED]
Also used in Middle English for “sinner, rascal, impious person” (late 13c.). Meaning “jester, court clown” in English is attested c. 1300, though it is not always possible to tell whether the reference is to a professional entertainer counterfeiting mental weakness or an amusing lunatic, and the notion of the fool sage whose sayings are ironically wise is also in English from c. 1300.
There is no foole to the olde foole
Proverbs of John Heywood, 1546
To make a fool of (someone) “cause to appear ridiculous” is from 1620s (make fool “to deceive, make (someone) appear a fool” is from early 15c.).
Feast of Fools (early 14c., from Medieval Latin festum stultorum) was the burlesque festival celebrated in some churches on New Year’s Day in medieval times.
Fool’s paradise “illusory state of happiness” is from mid-15c.
