an indicator that announces which electrical circuit has been active (as on a telephone switchboard) | a device for showing the operating condition of some system |
| 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 |
| a signal for attracting attention |
| (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 |