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"