kneecap
kneecap , noun
1.
(Anatomy) A roundish, flattened, sesamoid bone in the tendon in front of the knee joint; the patella; the kneepan.
2.
A cap or protection for the knee.
kneecap , transitive verb
to break the knees of, especially by shooting in the kneecap; -- often done by criminal or terrorist groups as a warning or punishment.