menarche

noun

Etymology: First attested 1900, from German Menarche, formed from meno- + -arche.

1. The onset of menstruation; a girl's first period.

   “How old is she? Nine? Ten? The menarche is not far off – a hint of a bosom, poor child.”

   “The most potent and indeed dangerous of all menstrual blood was the menarche, the first day's flow of the first menstruation of a virgin girl.”