ankle vs articulatio plana

ankle and articulatio plana both are nouns.

Word	Noun	Adjective	Verb	Adverb
ankle	Yes	No	No	No
articulatio plana	Yes	No	No	No

As nouns, articulatio plana is a hypernym of ankle; that is, articulatio plana is a word with a broader meaning than ankle:

ankle: a gliding joint between the distal ends of the tibia and fibula and the proximal end of the talus
articulatio plana: a freely moving joint in which the articulations allow only gliding motions

Other hypernyms of ankle include gliding joint.

ankle (noun)	articulatio plana (noun)
a gliding joint between the distal ends of the tibia and fibula and the proximal end of the talus	a freely moving joint in which the articulations allow only gliding motions