Merriam-Webster's Collegiate® Dictionary, 11th Edition
NUT
I. noun
Etymology: Middle English nute, note, from Old English hnutu; akin to Old High German nuz nut and perhaps to Latin nux nut Date: before 12th century
1. a. a hard-shelled dry fruit or seed with a separable rind or shell and interior kernel, the kernel of a nut, a dry indehiscent one-seeded fruit with a woody pericarp,
2. a hard problem or undertaking, core , heart , a perforated block usually of metal that has an internal screw thread and is used on a bolt or screw for tightening or holding something, the ridge in a stringed instrument (as a violin) over which the strings pass on the upper end of the fingerboard, a small lump (as of butter),
6. a foolish, eccentric, or crazy person, enthusiast , nonsense , a person's head, testis , the amount of money that must be earned in order to break even, en 1, nutlike adjective
II. intransitive verb (nutted; nutting)
Date: 1604
to gather or seek nuts