fool (n.1) Look up fool at Dictionary.com
late 13c., "silly or stupid 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." But 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]
Meaning "jester, court clown" in English is first attested late 14c., though it is not always possible to tell whether the reference is to a professional entertainer counterfeiting mental weakness or an amusing lunatic. The French word probably also got into English via its borrowing in the Scandinavian languages of the vikings (Old Norse fol, Old Danish fool, fol).
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. 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 gold "iron pyrite" is from 1829. Fool's paradise "illusory state of happiness" is from mid-15c. Fool-trap is from 1690s. Foolosopher, a useful insult, is in a 1549 translation of Erasmus. Fool's ballocks is described in OED as "an old name" for the green-winged orchid.
fool (v.) Look up fool at Dictionary.com
mid-14c., "to be foolish, act the fool," from fool (n.1). The transitive meaning "make a fool of" is recorded from 1590s. Sense of "beguile, cheat" is from 1640s. Also as a verb 16c.-17c. was foolify. Related: Fooled; fooling. Fool around is 1875 in the sense of "pass time idly," 1970s in sense of "have sexual adventures."
fool (adj.) Look up fool at Dictionary.com
"foolish, silly," from fool (n.1). Considered modern U.S. colloquial but attested in early 13c. and the modern use might be a survival of this.
fool (n.2) Look up fool at Dictionary.com
type of custard dish, 1590s, of uncertain origin. The food also was called trifle, which may be the source of the name (via verb and noun senses of fool). OED utterly rejects derivation from Old French fole "a pressing."