kneecap

Short definition from Wiktionary

Noun

1. 1
   The flat, roundish bone in the knee.
2. 2
   A metal cover trim that fits over a panel rib after it has been cut and bent.
3. 3
   A cap or strong covering for the knees, used chiefly for horses, to protect their knees in case of a fall.

Verb

1. 1
   To destroy the knees of (a person), usually by shooting at the knees, as a punishment carried out by criminals or terrorists.
2. 2
   To attack (someone) in a way that is excessively and needlessly damaging: To cut (someone) off at the knees.