menarche

plural menarches

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.

   1973, Patrick O'Brian, HMS Surprise

   2 more examples

   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.

   1978, Benjamin Walker, Encyclopedia of Metaphysical Medicine, Routledge, page 252

   Initiation is imagined, but the initiate is not the young girl in menarche, about to be wed to the moon, but a young man about to become a great hunter.

   1981, William Irwin Thompson, The Time Falling Bodies Take to Light: Mythology, Sexuality and the Origins of Culture, London: Rider/Hutchinson & Co., page 102

   Synonyms: menophania · Antonyms: menopause