n.
     - a person or device that monitors something.
 - a television receiver used in a studio to view the picture being transmitted from a particular camera. 
▸a screen which displays an image generated by a computer.
 ▸a loudspeaker used by performers on stage to hear themselves or in a studio to hear what has been recorded.
 - a school pupil with disciplinary or other special duties.
 - 
(also monitor lizard)
 a large tropical lizard with a long neck and a short body, formerly believed to give warning of crocodiles. 
[Genus Varanus: many species.]
 - historical a shallow-draught warship mounting one or two heavy guns for bombardment.
 
v.
 observe and check over a period of time. 
▸maintain regular surveillance over.
 ▸listen to and report on (a radio broadcast or telephone conversation).
 
  Derivative
  
    - monitorial adj.
  - monitorship n.
 
   
  Etymology
  C16: from L., from monit-, monere ‘warn’.