noun

1. Someone who watches over something; a person in charge of something or someone.

   “The camp monitors look after the children during the night, when the teachers are asleep.”

2. A device that detects and informs on the presence, quantity, etc., of something.

3. A device similar to a television set used as to give a graphical display of the output from a computer.

   “The information flashed up on the monitor.”

verb

1. To watch over; to guard.

Synonyms: oversee, supervise, track