The definition of a monster is a badly behaved or cruel person, something that is absurdly large, or a fictional and frightening creature.
(noun)See monster in Webster's New World College Dictionary
noun
Origin: ME monstre < OFr < L monstrum, divine portent of misfortune, monster < monere, to admonish, warn: see monitor
adjective
See monster in American Heritage Dictionary 4
noun
Origin:
Origin: Middle English monstre
Origin: , from Old French
Origin: , from Latin mōnstrum, portent, monster
Origin: , from monēre, to warn; see men-1 in Indo-European roots
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