menstruum vs menses

menstruum and menses both are nouns.

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

As nouns, menstruum and menses are synonyms defined as:

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

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

menstruum (noun)	menses (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
(archaic) a solvent