The Collaborative International Dictionary of English v.0.48:

Contestant \Con*test"ant\, n. [Cf. F. contestant.]
   One who contests; an opponent; a litigant; a disputant; one
   who claims that which has been awarded to another.
   [1913 Webster]

WordNet (r) 3.0 (2006):

contestant
    n 1: a person who participates in competitions
    2: a person who dissents from some established policy [syn:
       dissenter, dissident, protester, objector,
       contestant]