NOUN (1)

1. a person who is opposed (to an action or policy or practice etc.);
- Example: "the antis smelled victory after a long battle"


ADJECTIVE (1)

1. not in favor of (an action or proposal etc.);

The Collaborative International Dictionary of English v.0.48:

Anti \An"ti\ [Gr. 'anti` against. See Ante.]
   A prefix meaning against, opposite or opposed to, contrary,
   or in place of; -- used in composition in many English words.
   It is often shortened to ant-; as, antacid, antarctic.
   [1913 Webster]

WordNet (r) 3.0 (2006):

anti
    adj 1: not in favor of (an action or proposal etc.) [ant: pro]
    n 1: a person who is opposed (to an action or policy or practice
         etc.); "the antis smelled victory after a long battle"