Definition of monitor

• n. - One who admonishes; one who warns of faults, informs of duty, or gives advice and instruction by way of reproof or caution.
• n. - Hence, specifically, a pupil selected to look to the school in the absence of the instructor, to notice the absence or faults of the scholars, or to instruct a division or class.
• n. - Any large Old World lizard of the genus Varanus; esp., the Egyptian species (V. Niloticus), which is useful because it devours the eggs and young of the crocodile. It is sometimes five or six feet long.
• n. - An ironclad war vessel, very low in the water, and having one or more heavily-armored revolving turrets, carrying heavy guns.
• n. - A tool holder, as for a lathe, shaped like a low turret, and capable of being revolved on a vertical pivot so as to bring successively the several tools in holds into proper position for cutting.