1. (especially formerly) a student appointed to assist in the conduct of a class or school, as to help take attendance or keep order.
  2. a person appointed to supervise students, applicants, etc., taking an examination, chiefly to prevent cheating; proctor.
  3. a person who admonishes, especially with reference to conduct.
  4. something that serves to remind or give warning.
  5. a device or arrangement for observing, detecting, or recording the operation of a machine or system, especially an automatic control system.
  6. an instrument for detecting dangerous gases, radiation, etc.
  7. Radio and Television.
    1. a receiving apparatus used in a control room, especially to provide a steady check of the quality of an audio or video transmission.
    2. 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.
    3. any such receiving apparatus used in a closed-circuit system, as in an operating room.
  8. Computers.
    1. the screen component of a computer, especially a free-standing screen.
    2. a control program.Compare operating system.
    3. a group of systems used to measure the performance of a computer system.
  9. Nautical.
    1. a former U.S. steam-propelled, armored warship of very low freeboard, having one or more turrets and used for coastal defense.
    2. (initial capital letter, italics)the first of such warships, used against the Confederate ironclad warship Merrimac at Hampton Roads, Va., in 1862.
  10. 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.
  11. 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.
  12. Also called giant. (in hydraulic mining) a nozzle for dislodging and breaking up placer deposits with a jet of water.
  13. 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.

verb (used with object)

  1. Radio and Television.
    1. to listen to (transmitted signals) on a receiving set in order to check the quality of the transmission.
    2. to view or listen to (television or radio transmissions) in order to check the quality of the video or audio.
    3. to listen to (a radio conversation or channel); keep tuned to.
  2. to observe, record, or detect (an operation or condition) with instruments that have no effect upon the operation or condition.
  3. to oversee, supervise, or regulate: to monitor the administering of a test.
  4. to watch closely for purposes of control, surveillance, etc.; keep track of; check continually: to monitor one’s eating habits.

verb (used without object)

  1. to serve as a monitor, detector, supervisor, etc.


  1. a person or piece of equipment that warns, checks, controls, or keeps a continuous record of something
  2. education
    1. a senior pupil with various supervisory duties
    2. a pupil assisting a teacher in classroom organization, etc
  3. a television screen used to display certain kinds of information in a television studio, airport, etc
  4. the unit in a desk computer that contains the screen
    1. a loudspeaker used in a recording studio control room to determine quality or balance
    2. a loudspeaker used on stage to enable musicians to hear themselves
  5. a device for controlling the direction of a water jet in fire fighting
  6. any large predatory lizard of the genus Varanus and family Varanidae, inhabiting warm regions of Africa, Asia, and AustraliaSee also Komodo dragon
  7. Also called: giant mining a nozzle for directing a high-pressure jet of water at the material to be excavated
  8. (formerly) a small heavily armoured shallow-draught warship used for coastal assault

verb (tr)

  1. to act as a monitor of
  2. to observe or record (the activity or performance) of (an engine or other device)
  3. to check (the technical quality of) (a radio or television broadcast)

n.1540s, “senior pupil at a school charged with keeping order, etc.,” from Latin monitor “one who reminds, admonishes, or checks,” also “an overseer, instructor, guide, teacher,” agent noun from monere “to admonish, warn, advise,” related to memini “I remember, I am mindful of,” and to mens “mind,” from PIE root *men- “to think” (see mind (n.)). The type of lizard so called because it is supposed to give warning of crocodiles (1826). Meaning “squat, slow-moving type of ironclad warship” (1862) so called from name of the first vessel of this design, chosen by the inventor, Swedish-born U.S. engineer John Ericsson (1803-1889), because it was meant to “admonish” the Confederate leaders in the U.S. Civil War. Broadcasting sense of “a device to continuously check on the technical quality of a transmission” (1931) led to special sense of “a TV screen displaying the picture from a particular camera.” v.1818, “to guide;” 1924, “to check for quality” (originally especially of radio signals), from monitor (n.). General sense from 1944. Related: Monitored; monitoring. n.

  1. A usually electronic device used to record, regulate, or control a process or system.

  1. A device that accepts video signals from a computer and displays information on a screen. Monitors generally employ cathode-ray tubes or flat-panel displays to project the image. See Note at pixel.
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