noun

• A pointer or index that indicates something.
• A meter or gauge.
• The needle or dial on such a meter.
• (chemistry) Any of many substances, such as litmus, used to indicate the concentration of a substance, or the degree of a reaction.
• (ecology) A plant or animal whose presence is indicative of some specific environment.
• (economics) A measure, such as unemployment rate, which can be used to predict economic trends.
• (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.
• A bird, the honeyguide.