The Collaborative International Dictionary of English v.0.48:

Participant \Par*tic"i*pant\, n.
   A participator; a partaker.
   [1913 Webster]

         Participants in their . . . mysterious rites. --Bp.
                                                  Warburton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Participant \Par*tic"i*pant\, a. [L. participans, p. pr. of
   participare: cf. F. participant. See Participate.]
   Sharing; participating; having a share or part. --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

participant
    n 1: someone who takes part in an activity
    2: a person who participates in or is skilled at some game [syn:
       player, participant]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "participant":
   a party to, accessory, accomplice, actor, aide, assistant,
   colleague, confrere, contributor, copartner, cotenant, engaged,
   fellow, helper, implicated, involved, partaker, partaking,
   participating, participative, participator, participatory, partner,
   party, prime mover, shareholder, sharer, sharing