■ noun
1》 a thing that indicates a state or level.
2》 a gauge or meter of a specified kind.
3》 Brit. a flashing light on a vehicle to show that it is about to change lanes or turn.
4》 Brit. an information board or screen in a railway station, airport, etc.
5》 Chemistry a compound which changes colour at a specific pH value or in the presence of a particular substance, and can be used to monitor a chemical change.