oligomenorrhea vs menstruation

oligomenorrhea and menstruation both are nouns.

Word	Noun	Adjective	Verb	Adverb
oligomenorrhea	Yes	No	No	No
menstruation	Yes	No	No	No

As nouns, menstruation is a hypernym of oligomenorrhea; that is, menstruation is a word with a broader meaning than oligomenorrhea:

oligomenorrhea: abnormally light or infrequent menstruation
menstruation: the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause

Other hypernyms of oligomenorrhea include catamenia, flow, menses, menstruum, period.

oligomenorrhea (noun)	menstruation (noun)
abnormally light or infrequent menstruation	the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause