spheroid joint vs diarthrosis

spheroid joint and diarthrosis both are nouns.

Word	Noun	Adjective	Verb	Adverb
spheroid joint	Yes	No	No	No
diarthrosis	Yes	No	No	No

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

spheroid joint: a freely moving joint in which a sphere on the head of one bone fits into a rounded cavity in the other bone
diarthrosis: a joint so articulated as to move freely

Other hypernyms of spheroid joint include articulatio synovialis, synovial joint.

spheroid joint (noun)	diarthrosis (noun)
a freely moving joint in which a sphere on the head of one bone fits into a rounded cavity in the other bone	a joint so articulated as to move freely