Learner's definition of LAVATORY
1 formal : a room with a toilet and sink
◊ In U.S. English, lavatory is most often used for a room in an airplane.
It may also be used for a room in other kinds of public places.
In British English, lavatory is most often used for a room in a public place but may also be used for a room in a home.
3 US, technical : a bathroom sink