in|di|ca|tor

in|di|ca|tor «IHN duh _KAY tuhr», noun.

1. a person or thing that indicates.

2. a pointer on a dial that shows the amount of heat, pressure, speed, or other factor under measurement.

3. a measuring or recording instrument.

4. an index of business activity: »

The stock market's most widely used indicator [is] the Dow-Jones average of the prices of 30 major industrial companies' shares (Wall Street Journal).

5. a substance used to indicate chemical conditions or changes, usually by a change in color. Litmus paper is an indicator.

6. Chemistry. a tracer: »

a radioactive indicator.

7. Ecology. a) a species of animal or plant whose existence in an area is indicative of specific environmental conditions. b) an organism at or near the top of a food chain that reflects or indicates the lower levels in the chain by the food residues found in its body.