/ ˈmɒnstə(r); NAmE ˈmɑːn-/ noun , adjective
■ noun
1.
(in stories) an imaginary creature that is very large, ugly and frightening :
a monster with three heads
prehistoric monsters
2.
an animal or a thing that is very large or ugly :
Their dog's an absolute monster!
3.
a person who is very cruel and evil
4.
( humorous ) a child who behaves badly
■ adjective
[ only before noun ] ( informal ) unusually large
SYN giant :
monster mushrooms
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WORD ORIGIN
late Middle English : from Old French monstre , from Latin monstrum portent or monster, from monere warn.