As I understand the two terms:-
1. Monitor means a person or an instrument to keep a watch over proceedings and possibly alert people responsible to the fact that work is perhaps not happening as it should. So it's role is passive.
2. Whereas, a supervisor implies a person who is responsible to ensure that work is done as per program and, if it does not so happen, take corrective measures to ensure success. It is an active role.
Examples: A student may be made a class monitor or an electronic device may keep track of a patient's progress. Both can raise an alarm but may not be able to intervene and correct. A supervisor on the other hand would be responsible for both monitoring the progress as well as correcting/making adjustments so as to achieve the desired aim.
Colonel Gahlot, Proprietor
From India, Delhi