1. (noun)ball-and-socket joint, spheroid joint, cotyloid joint, enarthrodial joint, enarthrosis, articulatio spheroidea a freely moving joint in which a sphere on the head of one bone fits into a rounded cavity in the other bone Synonyms: enarthrosis, ball-and-socket joint, cotyloid joint, articulatio spheroidea, enarthrodial joint, spheroidjoint