<p><strong>Noun</strong></p><ul><li>(especially formerly) a student appointed to assist in the conduct of a class or school, as to help take attendance or keep order</li><li>a person appointed to supervise students, applicants, etc., taking an examination, chiefly to prevent cheating; proctor</li><li>a person who admonishes, especially with reference to conduct</li><li>something that serves to remind or give warning</li><li>a device or arrangement for observing, detecting, or recording the operation of a machine or system, especially an automatic control system</li><li>an instrument for detecting dangerous gases, radiation, etc.</li><li>Radio and Television: a receiving apparatus used in a control room, especially to provide a steady check of the quality of an audio or video transmission</li><li>a similar apparatus placed in various parts of a studio so that an audience can watch a recorded portion of a show, the performer can see the various segments of a program, etc.</li><li>any such receiving apparatus used in a closed-circuit system, as in an operating room</li><li>Computers: the screen component of a computer, especially a free-standing screen</li><li>a control program</li><li>Compare operating system</li><li>a group of systems used to measure the performance of a computer system</li><li>Nautical: a former U.S. steam-propelled, armored warship of very low freeboard, having one or more turrets and used for coastal defense</li><li>(initial capital letter, italics) the first of such warships, used against the Confederate ironclad warship Merrimac at Hampton Roads, Va., in 1862</li><li>a raised construction straddling the ridge of a roof and having windows or louvers for lighting or ventilating a building, as a factory or warehouse</li><li>an articulated mounting for a nozzle, usually mechanically operated, which permits a stream of water to be played in any desired direction, as in firefighting or hydraulic mining</li><li>Also called giant</li><li>(in hydraulic mining) a nozzle for dislodging and breaking up placer deposits with a jet of water</li><li>any of various large lizards of the family Varanidae, of Africa, southern Asia, the East Indies, and Australia, fabled to give warning of the presence of crocodiles: several species are endangered</li></ul><p><strong>Verb (used with object)</strong></p><ul><li>Radio and Television: to listen to (transmitted signals) on a receiving set in order to check the quality of the transmission</li><li>to view or listen to (television or radio transmissions) in order to check the quality of the video or audio</li><li>to listen to (a radio conversation or channel); keep tuned to</li><li>to observe, record, or detect (an operation or condition) with instruments that have no effect upon the operation or condition</li><li>to oversee, supervise, or regulate: to monitor the administering of a test</li><li>to watch closely for purposes of control, surveillance, etc.; keep track of; check continually: to monitor one's eating habits</li></ul><p><strong>Verb (used without object)</strong></p><ul><li>to serve as a monitor, detector, supervisor, etc.</li></ul>