Any of several publications e.g. the "Christian Science Monitor".

(Freemasonry) A text of works or instruction which are not secret and may be written e.g. "Indiana Monitor and Freemasons' Guide".

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

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

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

A studio monitor or loudspeaker.

(computing) A program for viewing and editing.

(nautical) One of a class of relatively small armored warships with only one or two turrets (but often carrying unusually large guns for a warship of its size), usually designed for shore bombardment or riverine warfare rather than open-ocean combat. [from 1862]

A monitor lizard.

(engineering) 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.

A monitor nozzle.

(transitive) To watch over; to guard.