polar opposite

from The Collaborative International Dictionary of English v.0.48

Opposite \Op"po*site\, n.
   1. One who opposes; an opponent; an antagonist. [Obs.]
      [1913 Webster]

            The opposites of this day's strife.   --Shak.
      [1913 Webster]

   2. That which is opposed or contrary in character or meaning;
      as, sweetness and its opposite; up is the opposite of
      down.
      [1913 Webster +PJC]

            The virtuous man meets with more opposites and
            opponents than any other.             --Landor.
      [1913 Webster]

   {polar opposite} that which is conspicuously different in
      most important respects.
      [PJC]