menses vs menstruation

menses and menstruation both are nouns.

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

As nouns, menses and menstruation are synonyms defined as:

menses and menstruation: the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause

Other synonyms of menses include catamenia, flow, menstruum, period.

menses (noun)	menstruation (noun)
the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause	the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause