Nut definition

From < . Cognate with Latin , Dutch , Old High German (German ), Old Norse (Danish , Icelandic , , Swedish ) and West Frisian .

A hard-shelled seed.
A fastener: a piece of metal, usually square or hexagonal in shape, with a hole through it having machined internal threads, intended to be screwed onto a bolt or other threaded shaft.
A crazy person.
The head.
A testicle.
The amount of money necessary to set up some venture; set-up costs.
- 1971, Hunter S. Thompson, Fear and Loathing in Las Vegas, Harper Perennial (2005), page 11:
  
  My attorney was waiting in a bar around the corner. “This won't make the nut,” he said, “unless we have unlimited credit.”
A stash of money owned by an extremely rich investor, sufficient to sustain a high level of consumption if all other money is lost.
On string instruments such as guitars and violins, the small piece at the peghead end of the fingerboard that holds the strings at the proper spacing and, in most cases, the proper height.
En, a unit of measurement equal to half of the height of the type in use.
An extreme enthusiast, such as a gun nut or car nut.

loony, nutbag, nutcase, nutter bonce, noodle (See further synonyms under head) ball, bollock (taboo slang), nads