Definition of monster
1 a
:an animal or plant of abnormal form or structure
- a mythical monster
- a sea monster
b
:one who deviates from normal or acceptable behavior or character
- an immoral monster
2
:a threatening force
- the same monster — Destiny … that rolls every civilization to doom
- —W. L. Sullivan
3 a
:an animal of strange or terrifying shape
- visualize this scaleless monster, eight or nine feet long, sprawling in the shade by the side of the mud pools
- —W. E. Swinton
b
:one unusually large for its kind
- That truck is a monster.
4
:something monstrous;
especially
:a person of unnatural or extreme ugliness, deformity, wickedness, or cruelty
- His father was a monster who beat his children for no reason.
5
:one that is highly successful
- That movie was a monster at the box office.
