any nonverbal action or gesture that encodes a message | a device for showing the operating condition of some system |
any incitement to action | 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 |
an electric quantity (voltage or current or field strength) whose modulation represents coded information about the source from which it comes | 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 |