A joint of a finger when the fist is closed

A collar stay, collar stick, collar bone, collar tab, collar stiffener, or collar stiff is a shirt accessory consisting of a smooth strip of rigid material, rounded at one end and pointed at the other, inserted into specially made pockets on the underside of a shirt collar to stabilize the collar's points.

Meat from the leg, from the muscle Rectus femoris

Knuckle is a 2011 Irish documentary film about the secretive world of Irish Traveller bare-knuckle boxing.

Press or rub with the knuckles

Shoot a marble while keeping one's knuckles on the ground