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late 14c., "pertaining to menses," also (in astronomy) "monthly," from Old French menstruel, from Latin menstrualis "monthly," especially "of or having monthly courses," from menstruus "of a month, every month, monthly, pertaining to a month," from mensis "month" (see moon (n.)).
premenstrual pre·men·stru·al (prē-měn'strōō-əl)
Of or occurring in the period just before menstruation.
menstrual men·stru·al (měn'strōō-əl) or men·stru·ous (-əs)
Of or relating to menstruation.