WordNet (r) 3.0 (2006):

teammate
    n 1: a fellow member of a team; "it was his first start against
         his former teammates" [syn: teammate, mate]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "teammate":
   ace, amigo, associate, bedfellow, bedmate, benchfellow, birthmate,
   bosom buddy, buddy, bunkie, bunkmate, butty, camarade,
   chamberfellow, chum, classmate, clubmate, co-worker, colleague,
   comate, companion, company, compeer, comrade, confrere, consociate,
   consort, copartner, copemate, copesmate, couchmate, cradlemate,
   crony, cupmate, fellow, fellow student, fellow worker,
   general partner, girl friend, gossip, jailmate, mate, messmate,
   old crony, pal, pard, pardner, partner, pewmate, playfellow,
   playmate, roommate, schoolfellow, schoolmate, secret partner,
   shelfmate, shipmate, shopmate, side partner, sidekick, sidekicker,
   silent partner, sleeping partner, special partner, tablemate,
   tentmate, watchmate, waymate, workfellow, yokefellow, yokemate