The joint of a finger, particularly when made prominent by the closing of the fingers.
The kneejoint, or middle joint, of either leg of a quadruped, especially of a calf; -- formerly used of the kneejoint of a human being.
The joint of a plant.
The joining pars of a hinge through which the pin or rivet passes; a knuckle joint.
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; as, brass knuckles; -- called also knuckle duster.
To yield; to submit; -- used with down, to, or under.
You have to really be courageous about your instincts and your ideas. Otherwise you'll just knuckle under, and things that might have been memorable will be lost. Francis Ford Coppola
For most people, creativity is a serious business. They forget the telling phrase 'the play of ideas' and think that they need to knuckle down and work more. Often, the reverse is true. They need to play. Julia Cameron
I do think that some of us began to realize that this was going to be a long struggle that was going to go on for decades, and you'd have to knuckle down. A lot of people in our generation did that. They didn't drop out and run away. Julian Bond
It is mistaken to claim that global problems will be solved more quickly if only researchers would abandon their quest to understand the universe and knuckle down to work on an agenda of public or political concerns. These are not 'either/or' options - indeed, there is a positive symbiosis between them. Martin Rees