1. [n]  any of various large tropical carnivorous lizards of Africa Asia and Australia; fabled to warn of crocodiles
2. [n]  a piece of electronic equipment that keeps track of the operation of a system continuously and warns of trouble
3. [n]  electronic equipment that is used to check the quality or content of electronic transmissions
4. [n]  display consisting of a device that takes signals from a computer and displays them on a CRT screen
5. [n]  an iron-clad vessel built by Federal forces to do battle with the Merrimac
6. [n]  someone who gives a warning so that a mistake can be avoided
7. [n]  someone who supervises (an examination)
8. [v]  keep tabs on; keep an eye on; keep under surveillance

Monitor
An account of the launching of the U.S. Navy`s first ironclad ship, designed to help enforce the blockade of Southern ports during the Civil War. Although the Monitor engaged in only one battle--against the Merrimack, the Confederate Navy`s ironclad--its revolutionary design marked the beginning of a new stage of naval history.

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1. \Mon"i*tor\, n. [L., fr. monere. See {Monition}, and cf.
   {Mentor}.]
   1. One who admonishes; one who warns of faults, informs of
      duty, or gives advice and instruction by way of reproof or
      caution.
            You need not be a monitor to the king. --Bacon.
   2. 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.
   3. (Zo["o]l.) Any large Old World lizard of the genus
      {Varanus}; esp., the Egyptian species ({V. Niloticus}),
      which is useful because it devours the eggs and young of
      the crocodile. It is sometimes five or six feet long.
   4. [So called from the name given by Captain Ericson, its
      designer, to the first ship of the kind.] An ironclad war
      vessel, very low in the water, and having one or more
      heavily-armored revolving turrets, carrying heavy guns.
   5. (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.
   {Monitor top}, the raised central portion, or clearstory, of
      a car roof, having low windows along its sides.
   

2. \Mon"i*tor\, n.
   A monitor nozzle.
   

1. A cathode-ray tube and associated electronics connected to a computer's video output. A monitor may be either monochrome (black and white) or colour (RGB). Colour monitors may show either digital colour (each of the red, green and blue signals may be either on or off, giving eight possible colours: black, white, red, green, blue, cyan, magenta and yellow) or analog colour (red, green and blue signals are continuously variable allowing any combination to be displayed). Digital monitors are sometimes known as TTL because the voltages on the red, green and blue inputs are compatible with TTL logic chips.

See also gamut, multisync, visual display unit.

2. A programming language construct which encapsulates variables, access procedures and initialisation code within an abstract data type. The monitor's variable may only be accessed via its access procedures and only one process may be actively accessing the monitor at any one time. The access procedures are critical sections. A monitor may have a queue of processes which are waiting to access it.

3. A hardware device that measures electrical events such as pulses or voltage levels in a digital computer.

4. To oversee a program during execution. For example, the monitor function in the Unix C library enables profiling of a certain range of code addresses. A histogram is produced showing how often the program counter was found to be at each position and how often each profiled function was called.

Unix man page: monitor(3).

5. A control program within the operating system that manages the allocation of system resources to active programs.

6. A program that measures software performance.