an instrument or device used for observing, checking, or keeping a continuous record of a process or quantity.
a heart monitor
a student with disciplinary or other special duties during school hours.
show the hall monitor your pass
a television receiver used in a studio to select or verify the picture being broadcast from a particular camera.
Products which could use the display include camera viewfinders, projectors, monitors , television sets and headsets for the military, medical and simulation markets.
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.
A good example is the savannah monitor, an African monitor lizard weighing about ten pounds, which spends most of its day patrolling its territory for tasty insects.
a shallow-draft armored warship mounting one or two heavy guns for bombardment.
They were up against John Dahlgren's naval force of monitors and warships.