The Collaborative International Dictionary of English v.0.48:

Partner \Part"ner\, v. t.
   To associate, to join. [Obs.] --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Partner \Part"ner\ (p[aum]rt"n[~e]r), n. [For parcener,
   influenced by part.]
   1. One who has a part in anything with an other; a partaker;
      an associate; a sharer. "Partner of his fortune." --Shak.
      Hence:
      (a) A husband or a wife.
      (b) Either one of a couple who dance together.
      (c) One who shares as a member of a partnership in the
          management, or in the gains and losses, of a business.
          [1913 Webster]

                My other self, the partner of my life. --Milton.
          [1913 Webster]

   2. (Law) An associate in any business or occupation; a member
      of a partnership. See Partnership.
      [1913 Webster]

   3. pl. (Naut.) A framework of heavy timber surrounding an
      opening in a deck, to strengthen it for the support of a
      mast, pump, capstan, or the like.
      [1913 Webster]

   Dormant partner, or Silent partner. See under Dormant,
      a.
      [1913 Webster]

   Syn: Associate; colleague; coadjutor; confederate; partaker;
        participator; companion; comrade; mate.
        [1913 Webster]

WordNet (r) 3.0 (2006):

partner
    n 1: a person's partner in marriage [syn: spouse, partner,
         married person, mate, better half]
    2: an associate in an activity or endeavor or sphere of common
       interest; "the musician and the librettist were
       collaborators"; "sexual partners" [syn: collaborator,
       cooperator, partner, pardner]
    3: a person who is a member of a partnership
    v 1: provide with a partner
    2: act as a partner; "Astaire partnered Rogers"

Moby Thesaurus II by Grady Ward, 1.0:

222 Moby Thesaurus words for "partner":
   a party to, accessory, accompanier, accompanist, accompanyist,
   accomplice, accumulate, ace, act in concert, act together,
   affiliate, agglomerate, aggregate, aggroup, ally, alter ego,
   amalgamate, amass, amigo, assemble, assistant, associate,
   attendant, band, band together, batch, be in cahoots, be in league,
   bedfellow, bedmate, better half, birthmate, bosom buddy,
   bring together, buddy, bulk, bunch, bunch together, bunch up,
   bunkie, bunkmate, butty, cabal, camarade, cement a union,
   centralize, chamberfellow, chum, classmate, club, club together,
   clubmate, clump, cluster, coact, coalesce, cohort, collaborate,
   collaborator, colleague, collect, colligate, collocate, collude,
   comate, combine, come together, companion, companion piece,
   company, compare, compeer, compile, comrade, concert, concord,
   concur, confederate, confrere, conglomerate, consociate,
   consolidate, consort, conspire, cooperate, copartner, copemate,
   copesmate, corral, cotenant, couchmate, couple, cradlemate, crony,
   cumulate, cupmate, dig up, do business with, draw together,
   dredge up, drive together, federalize, federate, fellow,
   fellow student, friend, fuse, gang, gang up, gather, gather in,
   gather together, general partner, get heads together, get in,
   get together, girl friend, go in partners, go in partnership,
   go partners, gossip, group, hang together, harmonize, helper,
   helpmate, helpmeet, hold together, hook up, hook up with, husband,
   jailmate, join, join forces, join fortunes with, join in,
   join together, join up with, join with, juxtapose, keep together,
   league, league together, lump together, make common cause, make up,
   marry, mass, match, mate, merge, messmate, mobilize, muster,
   old crony, organize, pair, pair off, pal, pard, pardner, partaker,
   participant, participator, party, pewmate, play ball, playfellow,
   playmate, pull together, put heads together, put together, raise,
   rake up, rally, reciprocate, roommate, round up, schoolfellow,
   schoolmate, scrape together, secret partner, shareholder, sharer,
   shelfmate, shipmate, shopmate, side partner, sidekick, sidekicker,
   silent partner, sleeping partner, special partner, spouse,
   stand together, stand up with, tablemate, take up, team up,
   team up with, team with, teammate, tentmate, throw in together,
   throw in with, tie in, tie in with, tie up, tie up with, unionize,
   unite, unite efforts, unite with, watchmate, waymate, wed, whip in,
   wife, work together, workfellow, yokefellow, yokemate