noun

1. a person who advises, warns, or cautions
2. in some schools, a student chosen to help keep order, record attendance, etc.
3. something that reminds or warns
4. any of a family (Varanidae) of usually very large, flesh-eating lizards of Africa, S Asia, and Australia: from the notion that they warn of the presence of crocodiles
5. ☆

   Etymology: < the Monitor, first such ship, built in 1862

   Historical a heavily armored warship with a low, flat deck and heavy guns fitted in one or more revolving turrets
6. ☆ a mounting for a nozzle that allows a stream of water to be played in any direction, as in fire fighting
7. a person who monitors a foreign broadcast, etc.
8. any of various devices for checking or regulating the performance of machines, aircraft, guided missiles, etc.
9. an instrument for measuring radioactive contamination by means of the ionizing radiation being emitted
10. Comput. a video screen for displaying data, graphic images, etc.
11. Radio, TV a receiver or speaker, as in the control room of a broadcasting studio, for checking the quality of the transmission

Etymology: L < pp. of monere, to warn < IE *moni- < base *men-, to think > mind

transitive verb, intransitive verb

1. to watch or check on (a person or thing) as a monitor
2. to check on or regulate the performance of (a machine, airplane, etc.)
3. to test for radioactive contamination with a monitor
4. to listen in on (a foreign broadcast, telephone conversation, etc.) as for gathering political or military information
5. Radio, TV to check the quality of (transmission) with or as with a monitor