knuckle

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

• noun The prominence of the dorsal aspect of a joint of a finger, especially of one of the joints connecting the fingers to the hand.
• noun A rounded protuberance formed by the bones in a joint.
• noun A cut of meat centering on the carpal or tarsal joint, as of a pig.
• noun The part of a hinge through which the pin passes.
• noun A sharp angle formed by the meeting of two surfaces, especially two ship's timbers.
• noun Brass knuckles.
• transitive verb To press, rub, or hit with the knuckles.
• transitive verb To shoot (a marble) with the thumb over the bent forefinger.

from The Century Dictionary.

• To touch or strike with the knuckle; pommel.
• To bend the knuckles; hold the knuckles (that is, the hand) close to the ground, in playing marbles: usually with down.
• To apply one's self earnestly, as to a task; engage vigorously, as in work.
• To submit, as in a contest; give up; yield.
• noun A sharply bent loop, as of intestine, especially when imprisoned, as in a hernia.
• noun In mech., the swinging leaf or hook used for the coupling device in certain automatic car-couplings, particularly in the Janney or M. C. B. (master car-builders') type. A hole is usually provided in the knuckle so that the common link-coupling may be used with it.
• noun The joint of a finger, especially that between the metacarpal bone and the first phalanx.
• noun The knee or knee-joint.
• noun A joint, especially of veal, consisting of the part of the leg called the knee. It is the part of the animal which corresponds to the hock of a horse, or the human heel, together with more or less of the leg above this joint.
• noun The joint of a plant; a node.
• noun A joint of cylindrical form, with a pin as axis, as that by which the straps of a hinge are fastened together.
• noun In ship-building, an acute angle on some of the timbers.
• noun plural Pieces of metal, usually brass (hence specifically known as brass knuckles), worn by lawless persons over the knuckles to protect them in striking a blow, and also to make a blow more effective. See knuckle-duster.
• To apply one's self earnestly.

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

• intransitive verb To yield; to submit; -- used with down, to, or under.
• intransitive verb [Colloq.], [Colloq.] To apply one's self vigorously or earnestly to
• noun The joint of a finger, particularly when made prominent by the closing of the fingers.
• noun The kneejoint, or middle joint, of either leg of a quadruped, especially of a calf; -- formerly used of the kneejoint of a human being.
• noun obsolete The joint of a plant.
• noun (Mech.) The joining parts of a hinge through which the pin or rivet passes; a knuckle joint.
• noun (Shipbuilding) A convex portion of a vessel's figure where a sudden change of shape occurs, as in a canal boat, where a nearly vertical side joins a nearly flat bottom.
• noun Slang. A contrivance, usually of brass or iron, and furnished with points, worn to protect the hand, to add force to a blow, and to disfigure the person struck; -- called also knuckle duster, knuckles or brass knuckles.
• noun (Mach.) a hinge joint, in which a projection with an eye, on one piece, enters a jaw between two corresponding projections with eyes, on another piece, and is retained by a pin which passes through the eyes and forms the pivot.
• noun (Cookery) the lower part of a leg of veal, from the line of the body to the knuckle.
• transitive verb rare To beat with the knuckles; to pummel.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of the joints between the phalanges of the fingers.
• noun by extension A mechanical joint.
• noun A cut of meat.
• noun sports, billiards, snooker, pool The curved part of the cushion at the entrance to the pockets on a cue sports table.
• verb To apply pressure, or rub or massage with one's knuckles.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a joint of a finger when the fist is closed
• verb press or rub with the knuckles
• verb shoot a marble while keeping one's knuckles on the ground