cotyloid joint vs coxa

cotyloid joint and coxa both are nouns.

Word	Noun	Adjective	Verb	Adverb
cotyloid joint	Yes	No	No	No
coxa	Yes	No	No	No

As nouns, coxa is a hyponym of cotyloid joint; that is, coxa is a word with a more specific, narrower meaning than cotyloid joint:

cotyloid joint: a freely moving joint in which a sphere on the head of one bone fits into a rounded cavity in the other bone
coxa: the ball-and-socket joint between the head of the femur and the acetabulum

Other hyponyms of cotyloid joint include articulatio humeri, shoulder, shoulder joint, articulatio coxae, hip, hip joint.

cotyloid joint (noun)	coxa (noun)
a freely moving joint in which a sphere on the head of one bone fits into a rounded cavity in the other bone	the ball-and-socket joint between the head of the femur and the acetabulum