"the fruit of certain trees and shrubs which have the seed enclosed in a woody covering not opening when ripe," Middle English note, from Old English hnutu, from Proto-Germanic *hnut- (source also of Old Norse hnot, Dutch noot, Old High German hnuz, German Nuss "nut"), from PIE *kneu- "nut" (source also of Latin nux; see nucleus).

Sense of "testicle" is attested by 1915 (nuts). Nut-brown "brown as a ripe, dried nut" is from c. 1300 of animals; c. 1500 of complexions of women. The mechanical nut that goes onto a bolt is first recorded 1610s, from some fancied resemblance (nut was used of other small mechanical pieces since early 15c.). The figurative nuts and bolts "fundamentals" is by 1952. The American English slang sense of "amount of money required for something" is recorded by 1912.  

Meaning "crazy person, crank" is attested from 1903; British form nutter is attested by 1958. Nut-case "crazy person" is from 1959; nut-house "insane asylum" is by 1929. For more on this sense, see nuts. In slang, nut also meant "fashionable or showy young man of affected elegance" [OED], 1904.

"pine-cone," a sense now obsolete; also "edible seed-kernel of several species of pine," Old English pinhnyte; see pine (n.) + nut (n.).

also nutcracker, "instrument used for cracking hard-shelled nuts," 1540s, from nut (n.) + agent noun from crack (v.). Hence also "toy having a grotesque human head, in the mouth of which a nut is placed to be cracked by a screw or lever." The ballet was first performed in 1892, based on Dumas père's rendition of E.T.A. Hoffmann's 1816 story "Nussknacker und Mausekönig."

late 15c., "one who gathers nuts," from nut + -er (1). Meaning "crazy person" is British slang, by 1958, from nut + -er (3). Nuttery "mental hospital" is attested in slang from 1931; earlier it meant "place for storing nuts" (1881).

"action of gathering nuts," 1723, verbal noun from nut (v.) "to gather nuts" (c. 1600), from nut (n.).

1610s, "fruit of the tropical palm tree," from coco + nut. In reference to the dried, shredded flesh of the nut used in cookery and confections, by 1830. Meaning "the head" is slang from 1834. Coconut-oil is attested from 1829.

type of small bird living in holes in trees, mid-14c. (early 13c. as a surname), note-hach, probably so called from its habit of breaking open and eating nuts; from nut (n.) + second element related to hack (v.) and hatchet.

early 15c., "nut-like," from nut (n.) + -y (2); from 1660s as "abounding in nuts." Sense of "having the flavor of nuts" is by 1828. Slang meaning "crazy" is by 1898 (see nuts); earlier colloquial sense was "amorous, in love (with)," 1821. [Byron, in a slangy passage in "Don Juan" (1823) uses it of a beggar's doxy; a footnote defines it as "conjointly, amorous and fascinating."] Related: Nuttiness.