Definition of monitor noun from the Oxford Advanced Learner's Dictionary

  1. 1   a television screen used to show particular kinds of information; a screen that shows information from a computer The details of today's flights are displayed on the monitor. a PC with a 17-inch colour monitor see also VDU See related entries: Computer hardware, Film-making equipment, Watching TV
  2. 2a piece of equipment used to check or record something a heart monitor See related entries: Medical equipment
  3. 3a student in a school who performs special duties, such as helping the teacher See related entries: People in schools
  4. 4a person whose job is to check that something is done fairly and honestly, especially in a foreign country UN monitors declared the referendum fair.
  5. 5 a large tropical lizard (= a type of reptile) See related entries: Amphibians and reptiles
  6. Word Originearly 16th cent. (in sense (3)): from Latin, from monit- ‘warned’, from the verb monere. Sense (2) dates from the 1930s.Extra examples He was lying there hooked up to a heart monitor. The heart monitor shows the strength of your pulse. The security staff can see all the outside of the building on their CCTV monitors.
See the Oxford Advanced American Dictionary entry: monitor