nut

Multiple Entries:
  nut    NUT  

Concise Oxford English Dictionary © 2008 Oxford University Press:
nut/nʌt/

▶noun

• 1 a fruit consisting of a hard or tough shell around an edible kernel.

  ■ the hard kernel of such a fruit.

• 2 a small flat piece of metal or other material, typically square or hexagonal, with a threaded hole through it for screwing on to a bolt.

  ■ the part at the lower end of a violin bow with a screw for adjusting the tension of the hair.

• 3 informal a crazy or eccentric person.

  ■ an obsessive enthusiast or devotee.

• 4 informal a person's head.

• 5 a small lump of coal.

• 6 (nuts) vulgar slang a man's testicles.

• 7 the fixed ridge on the neck of a stringed instrument over which the strings pass.

▶verb (nuts, nutting, nutted)

• 1 Brit. informal butt with one's head.

• 2 (usu. as noun nutting) archaic gather nuts.

– phrases
do one's nut Brit. informal be extremely angry or agitated.
nuts and bolts informal the basic practical details.
a tough (or hard) nut to crack informal a problem or an opponent that is hard to solve or overcome.
use (or take) a sledgehammer to crack a nut informal use disproportionately drastic measures to deal with a simple problem.

– origin OE hnutu, of Gmc origin.

Concise Oxford English Dictionary © 2008 Oxford University Press:
NUT

▶abbreviation (in the UK) National Union of Teachers.