Definition of "annunciator"

Anything that announces something.

1. An officer in the church of Constantinople, whose business it was to inform the people of the festivals to be celebrated.  examples

A signalling device that shows which of several electrical circuits is active, especially such a device in a telephone switchboard.  examples

(UK, railways) A buzzer in a signal box that sounds when a train activates a treadle positioned on the track, and thus provides a warning or announcement of a nearby train.  examples