1. One who admonishes; one who warns of faults, informs of duty, or gives advice and instruction by way of reproof or caution. You need not be a monitor to the king. (bacon)
2. 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.
3. (Science: zoology) Any large old world lizard of the genus varanus; especially, 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.
4. called from the name given by Captain Ericson, its designer, to the first ship of the kind An ironclad war vessel, very low in the water, and having one or more heavily-armored revolving turrets, carrying heavy guns.
5. (Science: machinery) 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. Monitor top, the raised central portion, or clearstory, of a car roof, having low windows along its sides.
Origin: L, fr. Monere. See Monition, and cf. Mentor.