Monitor

Merriam-Webster Online Dictionary
monitor (noun)
1.
a) a student appointed to assist a teacher
b) one that warns or instructs
c) one that or is used in as - monitors monitoring
(1) a cathode-ray tube used for display (as of television pictures or computer information)
(2) a device for observing a biological condition or function
2.
- monitor lizard
3.
first ship of the type
a) a heavily armored warship formerly used in coastal operations having a very low freeboard and one or more revolving gun turrets
b) a small modern warship with shallow draft for coastal bombardment
4.
a raised central portion of a roof having low windows or louvers for providing light and air
monitor (verb)
transitive verb
to watch, keep track of, or check usually for a special purpose