Definition of: nut

(nut) noun
1. Bot. a A fruit consisting of a kernel or seed enclosed in a woody shell, as in the hazelnut, beechnut, or chestnut; also, the kernel of such fruit, especially when edible. b A hard, indehiscent, one–seeded pericarp resulting from a compound ovary.
2. Mech. A small block of metal having an internal screw thread so that it may be fitted upon a bolt, screw, or the like.
3. A person or matter difficult to deal with; a problem.
4. Slang The head.
5. Slang A crazy or irresponsible person.
6. The ridge at the upper end of the neck of stringed instruments, serving to elevate the strings; also, the adjustable end of a fiddle bow.
—v.i. nut·ted, nut·ting To seek or gather nuts. [OE hnutu]
—nut′ter noun
MECHANICAL NUTS
a. Hexagonal, soft.
b. Lock.
c. Hexagonal, slotted.
d. Square, plain.
e. Double–cupped.
f. Joint, untapped.
g. Castle.
h. Thumb.
i. Square, chamfered.