1a device used for observing, checking, or keeping a continuous record of something:a heart monitor
a person operating a monitor:a monitor aboard the vessel said he had measured radiation levels ten times the normal level
a person who observes a process or activity to check that it is carried out fairly or correctly, especially in an official capacity:the deployment of troops went ahead despite the shooting down of an EC monitor’s helicopterthe independent judicial monitor
a person who listens to and reports on foreign radio broadcasts and signals:radio monitors reported they heard the pilot say he was heading for Paris
2a television receiver used in a studio to select or verify the picture being broadcast from a particular camera:the playback can be displayed on an external television screen or monitor
a screen which displays an image generated by a computer.
a loudspeaker used by performers on stage to hear themselves or in the studio to hear what has been recorded:I was amazed at the quality of the sound coming from the monitors
3a school pupil with disciplinary or other special duties:he was a school monitor and a choir boy
4 (also monitor lizard) a large tropical Old World lizard with a long neck, narrow head, forked tongue, strong claws, and a short body. Monitors were formerly believed to give warning of crocodiles.Called goanna in Australia.
Family Varanidae and genus Varanus: many species. See also Komodo dragon
5 historical a shallow-draught warship mounting one or two heavy guns for bombardment.
observe and check the progress or quality of (something) over a period of time; keep under systematic review:equipment was installed to monitor air quality
maintain regular surveillance over:he was a man of routine and it was easy for an enemy to monitor his movements
listen to and report on (a foreign radio broadcast or a telephone conversation):listening devices were used to monitor conversationsit was not easy to discover exactly how many calls were monitored
check or regulate the technical quality of (a radio transmission or television signal):a sound assistant monitors the signal on headphones