Indicator

[in-di-key-ter] /ˈɪn dɪˌkeɪ tər/

noun
1.
a person or thing that indicates.
2.
a pointing or directing device, as a pointer on the dial of an instrument to show pressure, temperature, speed, volume, or the like.
3.
an instrument that indicates the condition of a machine or the like.
4.
an instrument for measuring and recording variations of pressure in the cylinder of an engine.
5.
Chemistry.

6.
Ecology. a plant, animal, or species that indicates, by its presence in a given area, the existence of certain environmental conditions.
/ˈɪndɪˌkeɪtə/
noun
1.
something that provides an indication, esp of trends See economic indicator
2.
a device to attract attention, such as the pointer of a gauge or a warning lamp
3.
an instrument that displays certain operating conditions in a machine, such as a gauge showing temperature, speed, pressure, etc
4.

5.
Also called blinker. a device for indicating that a motor vehicle is about to turn left or right, esp two pairs of lights that flash when operated or a pair of trafficators
6.
Also called dial gauge. a delicate measuring instrument used to determine small differences in the height of mechanical components. It consists of a spring-loaded plunger that operates a pointer moving over a circular scale
7.
(chem)

8.
(ecology) Also called indicator species

n.

1660s, from Late Latin indicator, agent noun from indicare (see indication). As a finger muscle, from 1690s.

indicator in·di·ca·tor (ĭn’dĭ-kā’tər)
n.

indicator
(ĭn’dĭ-kā’tər)
A chemical compound that changes color and structure when exposed to certain conditions and is therefore useful for chemical tests. Litmus, for example, is an indicator that becomes red in the presence of acids and blue in the presence of bases.