indicator

Etymology

From Late Latin indicātor (“one who points out”), from Latin indicō (“point out”); see indicate.

noun

1. A pointer or index that indicates something.
   These old indicators [at Earl's Court station] show the destination of the next train by the appearance of an illuminated arrow next to the station name. The arrow may indicate that a train is going to Wimbledon, but it gives no clue as to when. Now, however, the indicators are supplemented by dot matrix panels that not only say where but also when. Why aren't the old ones removed? Because they, like the whole station, are Grade II listed. 2012, Andrew Martin, Underground Overground: A passenger's history of the Tube, Profile Books, page 79
2. A meter or gauge.
3. The needle or dial on such a meter.
4. (chemistry) Any of many substances, such as litmus, used to indicate the concentration of a substance, or the degree of a reaction.
5. (ecology) A plant or animal whose presence is indicative of some specific environment.
6. (economics) A measure, such as unemployment rate, which can be used to predict economic trends.
7. (UK, Australia, New Zealand, Ireland, automotive) A turn signal; each of the flashing lights on each side of a vehicle which indicate a turn is being made to left or right, or a lane change etc.
8. A bird, the honeyguide.