monitor

noun

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.”

   “And oft, mild friend, to me thou art A monitor, though still; Thou speak'st a lesson to my heart, Beyond the preacher's skill.”

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. (dated)The command line interface of an operating system.
7. (Hong-Kong, Singapore, archaic)A student leader in a class.

   “So, as she did not like the masters to be prying about the play-ground out of school, she chose from among the biggest and most trustworthy of her pupils five monitors, who had authority over the rest of the Boys, and kept the unruly ones in order.”

   “But it was not so—at least, not always—for though they fell out among themselves, they united their forces against the common enemy—the monitors!”

   “He learned that a monitor should assist the teachers in distributing worksheets, maintaining class discipline, helping classmates in need and so on.”

8. A relatively small armored warship 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.
9. A monitor lizard (Varanus spp. and extinct relatives in family Varanidae).
10. 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 several tools successively into position.
11. A monitor nozzle.
12. (obsolete)One who admonishes; one who warns of faults, informs of duty, or gives advice and instruction by way of reproof or caution.

    “c. 1620, Francis Bacon, letter of advice to Sir George Villiers You need not be a monitor to your gracious master the king.”

    “There has been no lack of other monitors — a ticklish haysel, a flooded harvest all through the north […]”

13. (archaic)An ironclad.

verb

1. (transitive)To watch over; to guard.

   “Monitoring refers to keeping a watch over patients to ensure that they are practising what they have learnt about disability prevention correctly.”

   “During July 1989-February 1990 ambient SO₂, was monitored using a mobile station in the residential-commercial neighborhood of Copacabana.”

   “2002, Mark Baker, Garry Smith, GridRM: A Resource Monitoring Architecture for the Grid, in Manish Parashar (editor), Grid Computing - GRID 2002: Third International Workshop, Springer, LNCS 2536, page 268, A wide-area distributed system such as a Grid requires that a broad range of data be monitored and collected for a variety of tasks such as fault detection and performance monitoring, analysis, prediction and tuning.”

   “The NOAA monitors global temperatures and records on a monthly and an annual basis, not daily. […] Various parts of the world have been experiencing heatwaves and on Thursday the EU’s climate monitoring service said the world had experienced its hottest June on record last month.”

name

1. Any of several publications e.g. the "Christian Science Monitor".
2. A text of works or instruction which are not secret and may be written e.g. "Indiana Monitor and Freemasons' Guide".
3. The USS Monitor, the first ironclad warship of its type.