bit

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

• noun The sharp part of a tool, such as the cutting edge of a knife or ax.
• noun A pointed and threaded tool for drilling and boring that is secured in a brace, bitstock, or drill press.
• noun The part of a key that enters the lock and engages the bolt and tumblers.
• noun The tip of the mouthpiece on a pipe or a cigarette or cigar holder.
• noun The metal mouthpiece of a bridle, serving to control, curb, and direct an animal.
• noun Something that controls, guides, or curbs.
• transitive verb To place a bit in the mouth of (a horse, for example).
• transitive verb To check or control with or as if with a bit.
• transitive verb To make or grind a bit on (a key).
• idiom (have/take) To be uncontrollable; cast off restraint.
• noun A binary digit, having either the value 0 or 1, used to store or represent data.
• noun A small portion, degree, or amount.
• noun A brief amount of time; a moment.
• noun A short scene or episode in a theatrical performance.
• noun A bit part.
• noun An entertainment routine given regularly by a performer; an act.
• noun A particular kind of action, situation, or behavior.
• noun A matter being considered.
• noun Informal An amount equal to one eighth of a dollar.
• noun Chiefly British A small coin.
• idiom (a bit) To a small degree; somewhat.
• idiom (bit by bit) Little by little; gradually.
• idiom (do (one's) bit) To do one's part or contribute one's share.

from The Century Dictionary.

• noun The act of biting; a bite.
• noun The action of biting food; eating; grazing.
• noun The biting, cutting, or penetrating action of an edged weapon or tool.
• noun The biting, catching, holding, cutting, or boring part of a tool.
• noun A boring-tool used in a carpenter's brace.
• noun The metal part of a bridle which is inserted in the mouth of a horse, with the appendages (rings, etc.) to which the reins are fastened.
• noun The joint of an umbrella.
• noun A hammer used by masons for dressing granite and for rough picking.
• noun In music, a short piece of tube used to alter slightly the pitch of such wind-instruments as the trumpet, cornet-à-pistons, etc.
• noun A Middle English and Anglo-Saxon contraction of biddeth, third person singular indicative present of bid.
• noun A Middle English form of butt.
• noun Preterit and occasional past participle of bite.
• noun A portion of food bitten off; a mouthful; a bite.
• noun A morsel or a little piece of food.
• noun Hence A small quantity of food; a modicum or moderate supply of provisions: as, to take a bit and a sup.
• noun A small piece or fragment of anything; a small portion or quantity; a little: as, a bit of glass; a bit of land; a bit of one's mind.
• noun Crisis; nick of time.
• noun A small piece of ground; a spot.
• noun Any small coin: as, a fourpenny-bit; a six-penny-bit.
• noun Synonyms Scrap, fragment, morsel, particle, atom.
• noun An obsolete spelling of bitt.
• noun In mining: The cutting edge of a drill for boring rock by hand or by machine drilling.
• noun A sharpened steel bar used for drilling rock by hand or by machine.
• noun In ceramics, a small piece of stone for separating the pieces of pottery in the kiln: used before the invention of stilts, cock-spurs, and triangles. Ware so made was called bit-stone ware.