kneecap /(?)/

knee·cap

kneecap

n.
  1. A roundish, flattened, sesamoid bone in the tendon in front of the knee joint; the patella; the kneepan. (Anat.)
  2. A cap or protection for the knee.

kneecap

v. t.
  1. to break the knees of, especially by shooting in the kneecap; -- often done by criminal or terrorist groups as a warning or punishment.