1. The joint of a finger, particularly when made prominent by the closing of the fingers.
2. The kneejoint, or middle joint, of either leg of a quadruped, especially of a calf; formerly used of the kneejoint of a human being. With weary knuckles on thy brim she kneeled sadly down. (Golding)
3. The joint of a plant.
4. (Science: mechanics) The joining pars of a hinge through which the pin or rivet passes; a knuckle joint.
5. A convex portion of a vessels figure where a sudden change of shape occurs, as in a canal boat, where a nearly vertical side joins a nearly flat bottom.
6. 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; as, brass knuckles; called also knuckle duster. Knuckle joint, the lower part of a leg of veal, from the line of the body to the knuckle.
Origin: oe. Knokel, knokil, as. Cuncel; akin to D. Knokkel, OFries. Knokele, knokle, g. Knochel, Sw. Knoge, dan. Knokkel, g. Knochen bone, and perh. To E. Knock.