monitor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that admonishes, cautions, or reminds, especially with respect to matters of conduct.
• noun A pupil who assists a teacher in routine duties.
• noun A usually electronic device used to record, regulate, or control a process or system.
• noun A video display or speaker used in a production studio to check audio or video quality.
• noun Computers A device that accepts video signals from a computer and displays information on a screen; a video display.
• noun Computers A program that observes, supervises, or controls the activities of other programs.
• noun An articulated device holding a rotating nozzle with which a jet of water is regulated, used in mining and firefighting.
• noun A heavily ironclad warship of the 19th century with a low, flat deck and one or more gun turrets.
• noun A modern warship designed for coastal bombardment.
• intransitive verb To check the quality or content of (an electronic audio or visual signal) by means of a receiver.
• intransitive verb To check by means of an electronic receiver for significant content, such as military, political, or illegal activity.
• intransitive verb To keep track of systematically with a view to collecting information.
• intransitive verb To test or sample, especially on a regular or ongoing basis.
• intransitive verb To keep close watch over; supervise.
• intransitive verb To direct.
• intransitive verb To act as a monitor.

from The Century Dictionary.

• To be a monitor or adviser to; admonish.
• noun One who warns of faults or informs of duty; an admonisher; one who gives advice and instruction by way of reproof or caution; an admonisher.
• noun A senior pupil in a school appointed to instruct and look after a junior division or class; a pupil appointed to superintend other pupils; in some American colleges, a student appointed to keep a record of the attendance of the other students upon certain exercises, as morning prayers.
• noun 3. A constable or officer of the law.
• noun A backboard.
• noun [capitalized] In herpetology, the typical genus of Monitoridæ, so called because one of the species was fabled to admonish man of the presence of the crocodile of the Nile. Also called Varanus.
• noun A lizard of the genus Monitor or family Monitoridæ. See cut under Hydrosaurus.
• noun A heavily armored iron-clad steam-vessel with a very low free-board, of a type invented by Ericsson, carrying on deck one or more revolving turrets, each containing one or more great guns, and designed to combine the maximum of gun-power with the minimum of exposure: so called from the name of the first vessel of the type, which was built during the American civil war, and in 1862 arrested the destructive course of the Confederate iron-clad ram Merrimac.
• noun A raised part of a roof, usually fitted with openings for light and ventilation, as in a passenger-car or omnibus. See monitor-roof.
• noun In hydraulics, a device consisting of a universal-jointed pipe, to which is attached a nozle throwing a powerful stream of water: used in hydraulic mining and on fire-boats. See hydraulic mining, under hydraulic.
• noun A turret or tool-holder in a lathe. See turret, 6.
• noun Same as catamaran, 4.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who admonishes; one who warns of faults, informs of duty, or gives advice and instruction by way of reproof or caution.
• noun Hence, specifically, a pupil selected to look to the school in the absence of the instructor, to notice the absence or faults of the scholars, or to instruct a division or class.
• noun (Zoöl.) Any large Old World lizard of the genus Varanus; esp., the Egyptian species (Varanus Niloticus), which is useful because it devours the eggs and young of the crocodile. It is sometimes five or six feet long.
• noun An ironclad war vessel, very low in the water, and having one or more heavily-armored revolving turrets, carrying heavy guns.
• noun (Mach.) 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 successively the several tools in holds into proper position for cutting.
• noun A monitor nozzle.
• noun the raised central portion, or clearstory, of a car roof, having low windows along its sides.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Someone who watches over something; a person in charge of something or someone.
• noun computing A device similar to a television set used as to give a graphical display of the output from a computer.
• noun computing A program for viewing and editing, as in machine code monitor.
• noun UK A student leader in a class.
• noun nautical A class of relatively small armored warships designed for shore bombardment or riverine warfare rather than combat with other ships.
• noun archaic An ironclad.
• noun A monitor lizard.
• verb transitive To watch over; to guard.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a piece of electronic equipment that keeps track of the operation of a system continuously and warns of trouble
• noun someone who supervises (an examination)
• noun someone who gives a warning so that a mistake can be avoided
• verb keep tabs on; keep an eye on; keep under surveillance