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]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "candidate":
   addict, agent, also-ran, applicant, appointee, aspirant, aspirer,
   assignee, baby kisser, bidder, campaigner, claimant, collector,
   coveter, dark horse, defeated candidate, deputy, desirer, devotee,
   dud, entrant, fancier, favorite son, freak, hankerer, has-been,
   hopeful, lame duck, licensee, lover, nominee, office seeker,
   petitioner, political hopeful, possibility, postulant,
   presidential timber, prospect, runner, running mate, seeker,
   selectee, solicitant, solicitor, stalking-horse, stumper, suitor,
   suppliant, supplicant, votary, wanter, whistle-stopper, wisher,
   yearner



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CANDIDATE. One who offers himself or is offered by others for an office.