INDICATOR

n. 1 a person or thing that indicates. 2 a device indicating the condition of a machine etc. 3 a recording instrument attached to an apparatus etc. 4 a board in a railway station etc. giving current information. 5 a device (esp. a flashing light) on a vehicle to show that it is about to change direction. 6 a substance which changes colour at a given stage in a chemical reaction. 7 Physics & Med. a radioactive tracer.