大姨媽

大姨妈
dàyímā
  1. mother's eldest sister (older than one's mother)
  2. (coll.) (euphemism) Aunt Flo (i.e. menstrual period)

CEDICT

colloquial euphemistic

Entry Composition

1 大姨 dàyí
  1. aunt (mother's eldest sister)
  2. (respectful term of address for a woman who is about the age of one's mother)
2 媽 mā
  1. ma
  2. mom
  3. mother