monitor

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.

4. A studio monitor or loudspeaker.
5. A program for viewing and editing.

   a machine code monitor

6. A student leader in a class.
7. One of a class of relatively small armored warships designed for shore bombardment or riverine warfare rather than combat with other ships.
8. An ironclad.
9. A monitor lizard.
10. One who admonishes; one who warns of faults, informs of duty, or gives advice and instruction by way of reproof or caution.
11. A tool holder, as for a lathe, shaped like a low turret, and capable of being revolved on a vertical pivot so as to bring the several tools successively into position.
12. A monitor nozzle.

verb

To watch over; to guard.