Bathroom
From Memory Alpha, the free Star Trek reference
A bathroom, also known as a restroom, waste extraction, toilet facility, is a room generally contains a toilet, and may also contain any of the following: sink, shower/sonic shower or a bath tub. These fixtures are then connected to a sewage and waste reclamation system where they are recycled.
The microbrain from Velara III caused several malfunctions all over the USS Enterprise-D including locking two crewmembers in the programmers' restroom. (TNG: "Home Soil")
The holding cells aboard Deep Space 9 featured a restroom. (DS9: "Vortex")
In 2375, the USS Voyager faced a situation where it was functioning on a mere four lavatories. (VOY: "Bride of Chaotica!")
