A voltage
It would be called a vacancy, or a vacant (empty) room. unoccupied......i think
Slave/Housecarl room
vacant
If you are signing in an (otherwise) empty room the sound will echo around you and will possibly sound high-pitched. If you are signing in an empty room then the room isn't empty.
The name given to the room beneath a house is called a basement.
An empty room. If you start to fill it, it's no longer an empty room.
The Beautiful Room Is Empty was created in 1988.
The Weight of an Empty Room was created in 2004.
Because Of Reflection
In this case the room is a set, and the things are the elements of the set. Since the word thing equals o, that is that this room has no elements, is empty, and this room is called an empty set.
The "driving room" is appropriatly called the wheel house because that is where wheel is.
A wrecking ball.