knee joint vs ginglymus

knee joint and ginglymus both are nouns.

Word	Noun	Adjective	Verb	Adverb
knee joint	Yes	No	No	No
ginglymus	Yes	No	No	No

As nouns, ginglymus is a hypernym of knee joint; that is, ginglymus is a word with a broader meaning than knee joint:

knee joint: hinge joint in the human leg connecting the tibia and fibula with the femur and protected in front by the patella
ginglymus: a freely moving joint in which the bones are so articulated as to allow extensive movement in one plane

Other hypernyms of knee joint include ginglymoid joint, hinge joint.

knee joint (noun)	ginglymus (noun)
hinge joint in the human leg connecting the tibia and fibula with the femur and protected in front by the patella	a freely moving joint in which the bones are so articulated as to allow extensive movement in one plane