From WordNet (r) 1.6 [wn]:

  antithesis
       n 1: exact opposite; "his theory is the antithesis of mine"
       2: the juxtaposition of contrasting words or ideas to give a
          feeling of balance

Back in the dark ages of my early college career I helped to edit a news magazine called antithesis which deliberately placed itself in opposition to the established norms of the college campus.