ladies' room

noun3

1. •
   A room belonging to or intended for some or all women.

   • ...a hanging stair of fifty-one steps... leads to the main hall, ladies' room, and balconies. — 1825
2. •
   (historical) A waiting room in a railway station or other public building intended exclusively for women and usually including a separate women's lavatory.

   • ...Passenger House, containing ticket office, baggage room, ladies' room, gentlemen's room, water closet, say 50 feet by 20 feet... — 1856
3. •
   (euphemistic) A public restroom intended for use by females.

   • The women's toilet (as distinguished from the ladies' room in a speakeasy, the johnny at school, the little girls' room at a party in an apartment, and the wash-my-hands on a train) was clean enough. — 1935