The Collaborative International Dictionary of English v.0.48:

Candidate \Can"di*date\, n. [L. Candidatus, n. (because
   candidates for office in Rome were clothed in a white toga.)
   fr. candidatus clothed in white, fr. candiduslittering,
   white: cf. F. candidat.]
   One who offers himself, or is put forward by others, as a
   suitable person or an aspirant or contestant for an office,
   privilege, or honor; as, a candidate for the office of
   governor; a candidate for holy orders; a candidate for
   scholastic honors.
   [1913 Webster]

WordNet (r) 3.0 (2006):

candidate
    n 1: a politician who is running for public office [syn:
         campaigner, candidate, nominee]
    2: someone who is considered for something (for an office or
       prize or honor etc.) [syn: candidate, prospect]