mother superior vs prioress

mother superior and prioress both are nouns.

Word	Noun	Adjective	Verb	Adverb
mother superior	Yes	No	No	No
prioress	Yes	No	No	No

As nouns, mother superior and prioress are synonyms defined as:

Other synonyms of mother superior include abbess.

mother superior (noun)	prioress (noun)
the superior of a group of nuns	the superior of a group of nuns