When you need to urinate and you go to a room where a toilet is located, the room you go to is an example of a lavatory.
The toilet that you use to urinate into is an example of a lavatory.
Origin of lavatory
- Middle English piscina from Late Latin lavātōrium from lavātor launderer from Latin lavāre to wash leu(ə)- in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition