nut

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An indehiscent fruit having a single seed enclosed in a hard shell, such as an acorn or hazelnut.
• noun The usually edible seed of such a fruit.
• noun Any of various other usually edible seeds enclosed in a hard covering such as a seed coat or the stone of a drupe, as in a pine nut, peanut, almond, or walnut.
• noun A crazy or eccentric person.
• noun An enthusiast; a buff.
• noun Informal A difficult endeavor or problem.
• noun Slang The human head.
• noun A ridge of wood at the top of the fingerboard or neck of a stringed instrument, over which the strings pass.
• noun A device at the lower end of the bow for a stringed instrument, used for tightening the hairs.
• noun A small block of metal or wood with a central, threaded hole that is designed to fit around and secure a bolt or screw.
• noun The cost of launching a business venture.
• noun The operating expenses of a theater, theatrical production, or similar enterprise.
• noun Vulgar Slang A testicle.
• intransitive verb To gather or hunt for nuts.
• intransitive verb Vulgar Slang To ejaculate.

from The Century Dictionary.

• noun Loosely, a similar vegetable product, as a tuberous root (earth-nut, ground-nut), leguminous pod (peanut), or seed(physic-nut).
• noun In general, the lower end or heel of the bow: opposed to point or head.
• noun In Australia:
• noun See the extract.
• noun A daredevil.
• To gather nuts: used especially in the present participle.
• noun The fruit of certain trees and shrubs which have the seed inclosed in a bony, woody, or leathery covering, not opening when ripe.
• noun In machinery, some small part supposed in some way to resemble a nut.
• noun Same as chestnut-coal.
• noun plural Something especially agreeable or enjoyable.
• noun plural The testicles.
• noun A cup made of the shell of a cocoanut or some other nut, often mounted in silver.
• noun A bulbous plant, Iris Sisyrinchium, of southern Europe.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To gather nuts.
• noun (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.
• noun 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.
• noun The tumbler of a gunlock.
• noun (Naut.) A projection on each side of the shank of an anchor, to secure the stock in place.
• noun vulgar slang Testicles.
• noun 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.
• noun See under Buoy.
• noun screened coal of a size smaller than stove coal and larger than pea coal; -- called also chestnut coal.
• noun (Zoöl.) any leucosoid crab of the genus Ebalia as, Ebalia tuberosa of Europe.
• noun (Bot.) See nut grass in the vocabulary.
• noun a device, as a metal plate bent up at the corners, to prevent a nut from becoming unscrewed, as by jarring.
• noun (Bot.) See under Pine.
• noun (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.
• noun a tree that bears nuts.
• noun (Zoöl.) any species of weevils of the genus Balaninus and other allied genera, which in the larval state live in nuts.