knee vs kneecap

knee and kneecap both are nouns.

Word	Noun	Adjective	Verb	Adverb
knee	Yes	No	No	No
kneecap	Yes	No	Yes	No

knee (noun)	kneecap (noun)
joint between the femur and tibia in a quadruped; corresponds to the human knee	a small flat triangular bone in front of the knee that protects the knee joint
the part of a trouser leg that provides the cloth covering for the knee
hinge joint in the human leg connecting the tibia and fibula with the femur and protected in front by the patella

knee (verb)	kneecap (verb)
	shoot in the kneecap, often done by terrorist groups as a warning