a legendary animal combining features of animal and human form or having the forms of various animals in combination, as a centaur, griffin, or sphinx.
any creature so ugly or monstrous as to frighten people.
any animal or human grotesquely deviating from the normal shape, behavior, or character.
a person who excites horror by wickedness, cruelty, etc.
any animal or thing huge in size.
an animal or plant of abnormal form or structure, as from marked malformation or the absence of certain parts or organs.
a grossly anomalous fetus or infant, especially one that is not viable.
anything unnatural or monstrous.
huge; enormous; monstrous: a monster tree.

1250–1300; Middle English monstre < Latin mōnstrum portent, unnatural event, monster, equivalent to mon(ēre) to warn + -strum noun suffix

monsterlike, adjective

4. fiend, brute, demon, devil, miscreant. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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World English Dictionary
monster (ˈmɒnstə)
1.  an imaginary beast, such as a centaur, usually made up of various animal or human parts
2.  a person, animal, or plant with a marked structural deformity
3.  a cruel, wicked, or inhuman person
4.  a.  a very large person, animal, or thing
 b.  (as modifier): a monster cake
5.  informal (Austral), (NZ) to criticize (a person or group) severely
6.  (Austral), (NZ) sport to use intimidating tactics against (an opponent)
[C13: from Old French monstre, from Latin monstrum portent, from monēre to warn]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

c.1300, "malformed animal, creature afflicted with a birth defect," from O.Fr. monstre, from L. monstrum "monster, monstrosity, omen, portent, sign," from root of monere "warn" (see monitor). Abnormal or prodigious animals were regarded as signs or omens of impending evil.
Extended c.1385 to imaginary animals composed of parts of creatures (centaur, griffin, etc.). Meaning "animal of vast size" is from 1530; sense of "person of inhuman cruelty or wickedness" is from 1556. In O.E., the monster Grendel was an aglæca, a word related to aglæc "calamity, terror, distress, oppression."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

monster mon·ster (mŏn'stər)

  1. An animal, a plant, or other organism having structural defects or deformities.

  2. A fetus or an infant that is grotesquely abnormal and usually not viable.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Idioms & Phrases


see green-eyed monster.

The American Heritage® Dictionary of Idioms by Christine Ammer.
Copyright © 1997. Published by Houghton Mifflin.
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Encyclopedia Britannica


in biology, an embryo, a newborn animal, or young plant that is grossly deformed. The defects may be genetic (i.e., inherited) or result from such influences as drugs, X rays, or diseases. Two main types of monster are recognized: those with defective or excessive growth of body parts and those with partial or complete doubling of the body on one of its axes. The repetition or absence of body parts such as fingers or toes are frequent anomalies in humans and other mammals.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
It is one small step for science education, and one giant leap for monster kind.
The student-loan system has grown into an out-of-control monster tearing at the
  fabric of civil society.
There is nothing quite so frightening as the idea of a sea monster.
For example, animators will use it to determine how a patch of hair will move
  when a monster brushes up against an object.
Idioms & Phrases
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