The Collaborative International Dictionary of English v.0.48:

Overman \O"ver*man\, n.; pl. -men.
   1. One in authority over others; a chief; usually, an
      overseer or boss.
      [Webster 1913 Suppl.]

   2. An arbiter.
      [Webster 1913 Suppl.]

   3. In the philosophy of Nietzsche, a man of superior physique
      and powers capable of dominating others; one fitted to
      survive in an egoistic struggle for the mastery.
      [Webster 1913 Suppl.]