What is the meaning of Knuckle?

Any of the joints between the bones of the fingers.

A mechanical joint.

The curved part of the cushion at the entrance to the pockets on a cue sports table.

The kneejoint of a quadruped, especially of a calf; formerly, the kneejoint of a human being.

A cut of meat of various kinds.

The joint of a plant.

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.

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; a knuckle duster.

The rounded point where a flat changes to a slope on a piste.

To apply pressure, or rub or massage with one's knuckles (sense 1).

To strike or punch.

To bend the fingers.

To touch one's forehead as a mark of respect.

To yield.

To land on the knuckle (sense 9) of a curve of a slope, after a jump off a ramp that precedes the slope.

Source: wiktionary.org