Definition of "Monitor" :

noun: any of various large tropical carnivorous lizards of Africa and Asia and Australia; fabled to warn of crocodiles

noun: a piece of electronic equipment that keeps track of the operation of a system continuously and warns of trouble

noun: electronic equipment that is used to check the quality or content of electronic transmissions

noun: display produced by a device that takes signals and displays them on a television screen or a computer monitor

noun: an ironclad vessel built by Federal forces to do battle with the Merrimac

noun: someone who gives a warning so that a mistake can be avoided

noun: someone who supervises (an examination)

verb: keep tabs on; keep an eye on; keep under surveillance

"We are monitoring the air quality."

verb: check, track, or observe by means of a receiver