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"

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "anti":
   adversary, adversative, adverse, adversive, alien, antagonistic,
   antipathetic, antithetic, antonymous, at cross-purposes, balancing,
   clashing, compensating, competitive, con, conflicting, confronting,
   contradictory, contradistinct, contrapositive, contrarious,
   contrary, contrasted, converse, counter, counterbalancing,
   counterpoised, countervailing, cross, dead against, disaccordant,
   discordant, discrepant, dissentient, enemy, eyeball to eyeball,
   fractious, hostile, inconsistent, inimical, inverse, negative,
   noncooperative, obstinate, obverse, opponent, opposed, opposing,
   opposite, oppositional, oppositive, oppugnant, overthwart,
   perverse, recalcitrant, refractory, repugnant, reverse, rival,
   squared off, uncooperative, unfavorable, unfriendly,
   unpropitious