From The Collaborative International Dictionary of English v.0.48 [gcide]:
Monitor \Mon"i*tor\, n. [L., fr. monere. See Monition, and cf.
Mentor.]
1. One who admonishes; one who warns of faults, informs of
duty, or gives advice and instruction by way of reproof or
caution.
[1913 Webster]
You need not be a monitor to the king. --Bacon.
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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.
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3. (Zool.) Any large Old World lizard of the genus Varanus;
esp., the Egyptian species (Varanus Niloticus), which is
useful because it devours the eggs and young of the
crocodile. It is sometimes five or six feet long.
[1913 Webster]
4. [So 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.
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5. (Mach.) 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.
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6. A monitor nozzle.
[Webster 1913 Suppl.]
Monitor top, the raised central portion, or clearstory, of
a car roof, having low windows along its sides.
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From WordNet (r) 3.0 (2006) [wn]:
Varanus niloticus
n 1: destroys crocodile eggs [syn: African monitor, {Varanus
niloticus}]