Etymology of Menstruation
From the online Etymology dictionary:
Menstruation: c.1780, from menstruate + -ion. O.E. equivalent was monaðblot “month-blood.”
Menstrual: late 14c., from O.Fr. menstruel, from L. menstrualis “monthly,” especially “of or having monthly courses,” from menstruus “of menstruation, monthly,” from mensis “month” (see menses).
Menses: “monthly discharge of blood from the uterus,” 1590s, from L. menses, pl. of mensis “month” (see moon).
Moon: O.E. mona, from P.Gmc. *mænon- (cf. O.S., O.H.G. mano, O.Fris. mona, O.N. mani, Du. maan, Ger. Mond, Goth. mena “moon”), from PIE *me(n)ses- “moon, month” (cf. Skt. masah “moon, month;” Avestan ma, Pers. mah, Armenian mis “month;” Gk. mene “moon,” men “month;” L. mensis “month;” O.C.S. meseci, Lith. menesis “moon, month;” O.Ir. mi, Welsh mis, Bret. miz “month”), probably from base *me- “to measure,” in reference to the moon’s phases as the measure of time. In Greek, Italic, Celtic, Armenian the cognate words now mean only “month.” Gk. selene (Lesbian selanna) is from selas “light, brightness (of heavenly bodies).”
Pretty straightforward… no surprise there… interesting nonetheless.