n. 1. (Anat.) A roundish, flattened, sesamoid bone in the tendon in front of the knee joint; the patella; the kneepan. [ 1913 Webster ]
2. A cap or protection for the knee.
v. t. to break the knees of, especially by shooting in the kneecap; -- often done by criminal or terrorist groups as a warning or punishment. Syn. -- knee-cap. [ WordNet 1.5 ]