rotatory joint vs diarthrosis

rotatory joint and diarthrosis both are nouns.

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

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

rotatory joint: a freely moving joint in which movement is limited to rotation
diarthrosis: a joint so articulated as to move freely

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

rotatory joint (noun)	diarthrosis (noun)
a freely moving joint in which movement is limited to rotation	a joint so articulated as to move freely