- any plant or animal of abnormal shape or structure, as one greatly malformed or lacking some parts; monstrosity
- any imaginary or fictional creature regarded as unnatural, repulsive, terrifying, etc.
- something monstrous
- a person so cruel, wicked, depraved, etc. as to horrify others
- any huge animal
- Informal any huge thing
- Archaic a malformed fetus, esp. one with an excess or deficiency of limbs or parts
Origin of monsterMiddle English monstre from Old French from Classical Latin monstrum, divine portent of misfortune, monster from monere, to admonish, warn: see monitor