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"one who gathers nuts," late 15c., from nut + -er (1). Meaning "crazy person" is British slang, 1958, from nut + -er (3). Nuttery "mental hospital" is attested from 1931; earlier it meant "place for storing nuts" (1881).
A crazy person; nut, nutball: the Zodiac killer or some nutter on the loose/ Mick Jagger says there will always be the nutters
[1958+; a British coinage and still chiefly British; perhaps influenced by Nutter,trademark name of a butter made from nuts, found by 1906]