c.1275, from O.Fr.
fol "madman, insane person," also an adj. meaning "mad, insane," from L.
follis "bellows, leather bag," in V.L. used with a sense of "windbag, empty-headed person" (see
follicle). Cf. also Skt.
vatula- "insane," lit. "windy, inflated with wind."
"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]
Meaning "jester, court clown" first attested 1370, though it is not always possible to tell whether the reference is to a professional entertainer or an amusing lunatic on the payroll. As the name of a kind of custard dish, it is attested from 1598 (the food was also called
trifle, which may be the source of the name). The verb meaning "to make a fool of" is recorded from 1596.
Feast of Fools (c.1320), from M.L.
festum stultorum) refers to the burlesque festival celebrated in some churches on New Year's Day in medieval times.
Fool's gold "iron pyrite" is from 1882.
Fool's paradise "state of illusory happiness" is from 1462.
Fool around is 1875 in the sense of "pass time idly," 1970s in sense of "have sexual adventures."
Foolosopher, a most useful insult, turns up in a 1549 translation of Erasmus.
[fool] 
