There is a VERY interesting book titled From a Broken Web, by Catherine Keller. She reveals that the 'monster' motif begins proper with the 'heroic myths', and that really the essence of the meaning OF 'monster' for this solar-mythological patriarchal mindset is the female.
The 'hero' in affect creates what he fears, nature, and the deeper parts of his being. These dissociated parts become monsters to him which he then seeks to continually slay. This is still going on, escalatingly so, as we see more and more senseless wars, and ecocide from a warrior-based culture which worships the ancient warrior cultures.