It’s agreed by most that a monster is some type of creature, with some sort of negative connotation, whether it be appearance, personality, or intent. Originally, ‘monster’ was used to describe mythical creatures like centaurs, griffins, or sphinxes. In most stories, these so called ‘monsters’ actually provide help to humans, giving aid in the form of advice for brute force. For example, in the story The Lion, the Witch, and the Wardrobe, the main characters, four children, are find themselves in a mythical world, and throughout the story are helped by all sorts of ‘monsters’. Beavers that talk, a faun(half human, half goat), a centaur or two, and several gnomes. The protagonists receive the most help from a powerful lion, who talks and actually comes back to life. These monsters weren’t all that ‘monstrous’, originally. Just a creature a little on the strange side.
Slowly, however, it evolved into a more disturbing term, used to describe anything with grotesque or misshapen features. During the Middle Ages, children with deformities were thought to be possessed by demons, and therefore were considered monsters. Various religious groups and churches performed horrific forms of torture on the children, called exorcisms to try and rid them of their ‘demons’.
As horror stories became more popular, the term monster evolved