ant/anti:

is opposite, or opposes something else.

1. antagonist:

   a person who opposes, or is unfriendly toward another; an opponent.

2. antipathy:

   a strong dislike.

3. antithesis:

   the contrast, or opposition of ideas.

Cornog, M. (1994). Merriam-Webster's vocabulary builder. Springfield, Mass: Merrian-Webster.