a device for showing the operating condition of some system
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
the consequences of an event (especially a catastrophic event); "the aftermath of war"; "in the wake of the accident no one knew how many had been injured"
the lagging of an effect behind its cause; especially the phenomenon in which the magnetic induction of a ferromagnetic material lags behind the changing magnetic field