What is the opposite of anthropomorphism?
Depending on how you define the opposite of anthropomorphism, it could be one of a few words. I suggest zoomorphism, dehumanize, and deanthropomorphism as possibilities.
Anthropomorphism is the attribution of human-like qualities onto non-human subjects, such as inanimate objects, plants, animals, and the like.
There would then be a couple of different ways we could find a word meaning the opposite. One would be a word that refers to the attribution of animal-like qualities onto a human. That word is zoomorphism. Examples include calling someone a "dirty dog", a "skunk", a "snake", etc.
Another way to take the opposite would be to have a word that refers to the removal of human-like traits from a human. That word is dehumanize.
The last way I can see an opposite is by finding a word that refers to the removal of human-like traits from non-humans. I think the best word for that would be deanthropomorphism