The Collaborative International Dictionary of English v.0.48:

Nut \Nut\ (n[u^]t), n. [OE. nute, note, AS. hnutu; akin to D.
   noot, G. nuss, OHG. nuz, Icel. hnot, Sw. n["o]t, Dan.
   n["o]d.]
   [1913 Webster]
   1. (Bot.) The fruit of certain trees and shrubs (as of the
      almond, walnut, hickory, beech, filbert, etc.), consisting
      of a hard and indehiscent shell inclosing a kernel.
      [1913 Webster]

   2. A perforated block (usually a small piece of metal),
      provided with an internal or female screw thread, used on
      a bolt, or screw, for tightening or holding something, or
      for transmitting motion. See Illust. of 1st Bolt.
      [1913 Webster]

   3. The tumbler of a gunlock. --Knight.
      [1913 Webster]

   4. (Naut.) A projection on each side of the shank of an
      anchor, to secure the stock in place.
      [1913 Webster]

   5. pl. Testicles. [vulgar slang]
      [PJC]

   Check nut, Jam nut, Lock nut, a nut which is screwed up
      tightly against another nut on the same bolt or screw, in
      order to prevent accidental unscrewing of the first nut.


   Nut buoy. See under Buoy.

   Nut coal, screened coal of a size smaller than stove coal
      and larger than pea coal; -- called also chestnut coal.


   Nut crab (Zool.), any leucosoid crab of the genus Ebalia
      as, Ebalia tuberosa of Europe.

   Nut grass (Bot.), See nut grass in the vocabulary.

   Nut lock, a device, as a metal plate bent up at the
      corners, to prevent a nut from becoming unscrewed, as by
      jarring.

   Nut pine. (Bot.) See under Pine.

   Nut rush (Bot.), a genus of cyperaceous plants (Scleria)
      having a hard bony achene. Several species are found in
      the United States and many more in tropical regions.

   Nut tree, a tree that bears nuts.

   Nut weevil (Zool.), any species of weevils of the genus
      Balaninus and other allied genera, which in the larval
      state live in nuts.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nut tree
    n 1: tree bearing edible nuts