IPA: /mɪˈnɑːrki/
KK: /mɛnˈɑrki/
The first time a girl has her menstrual period, which usually happens during her teenage years as she grows up.
Menarche typically occurs between the ages of 9 and 16.
Menarche is formed from "men" (from Greek "mēn", meaning month) and "archē" (from Greek "archē", meaning beginning or origin). The term refers to the first occurrence of menstruation, marking the beginning of a female's reproductive capability.
Think of 'month' ('men') as it relates to the 'beginning' ('archē') of a new phase in life — menarche signifies the start of monthly menstrual cycles.