menstrual

From Middle English menstruall, borrowed from Latin mēnstruālis, itself from mēnstrua ("menses"), the neuter plural of mēnstruus, meaning "monthly" or "of a month." That in turn traces back to mēnsis, "month."

The word narrowed over time from a general Latin sense of "monthly" to its specific modern meaning tied to the menstrual cycle.

Mēnsis, the Latin root for "month," connects this word back to "moon" — the timekeeper whose cycle first gave humans the idea of a month.