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"nut with flared sides for turning with the thumb and forefinger;" so called for its shape. Meaning "weird person" recorded by 1989, probably not from the literal sense but from the secondary sense of nut, influenced perhaps by slang senses of wing in wing-ding "wild party," originally "fit, spasm" (1937). An earlier, British, sense of wingnut was "person with large, protruding ears" (1986).
A weird or insane person; weirdo, Nutcase: Too weird for me. You guys are wingnuts
[1980s+; probably fr wingy and nut]
(genus Pterocarya), any of about six species of Asian trees of the walnut family (Juglandaceae). They often are 30 m (about 100 feet) tall and bear winged, edible, one-seeded nuts. One species, P. stenoptera, is planted as an ornamental. The wood of some species is used in cabinetmaking.