'menstr-' originates from Latin, specifically from words such as 'menstruus' and 'mensis' (often recorded as 'menstrua' or 'mensis'), where 'mensis' meant 'month' and 'menstruus' meant 'monthly' or 'of a month'.

'menstr-' developed from Latin 'mensis' (meaning 'month') and the adjective 'menstruus' ('monthly'); these Latin forms gave rise to Medieval and Modern Latin words like 'menstruatio', which passed into English as 'menstruation' (via direct borrowing from Latin or through French-influenced medical Latin).

Initially it related broadly to 'month' or 'monthly'; over time the sense narrowed in English to denote the monthly physiological bleeding in uterine cycles and adjectives describing that process.