1.Definition: (chemistry) a substance that changes color to indicate the presence of some ion or substance; can be used to indicate the completion of a chemical reaction or (in medicine) to test for a particular reaction

Category: General

2.Definition: a device for showing the operating condition of some system

Category: Objects

3.Definition: a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time

Related Noun(s):index, indicant

Category: General

4.Definition: a signal for attracting attention

Category: General