The Collaborative International Dictionary of English v.0.48:

Supplant \Sup*plant"\, v. t. [imp. & p. p. Supplanted; p. pr.
   & vb. n. Supplanting.] [F. supplanter, L. supplantare to
   trip up one's heels, to throw down; sub under + planta the
   sole of the foot, also, a sucker, slip, sprout. Cf. Plant,
   n.]
   1. To trip up. [Obs.] "Supplanted, down he fell." --Milton.
      [1913 Webster]

   2. To displace and take the place of; to supersede; to remove
      or displace by stratagem; as, a rival supplants another in
      the favor of a mistress or a prince.
      [1913 Webster]

            Suspecting that the courtier had supplanted the
            friend.                               --Bp. Fell.
      [1913 Webster]

   3. To overthrow, undermine, or force away, in order to get a
      substitute in place of. [obsolescent]
      [1913 Webster]

            You never will supplant the received ideas of God.
                                                  --Landor.
      [1913 Webster]

   4. To remove (a thing) and replace it with something else.
      [PJC]

   Syn: To remove; displace; overpower; undermine; overthrow;
        supersede.
        [1913 Webster]

WordNet (r) 3.0 (2006):

supplant
    v 1: take the place or move into the position of; "Smith
         replaced Miller as CEO after Miller left"; "the computer
         has supplanted the slide rule"; "Mary replaced Susan as the
         team's captain and the highest-ranked player in the school"
         [syn: supplant, replace, supersede, supervene upon,
         supercede]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "supplant":
   act for, bounce, cast out, change places with, crowd out, cut out,
   dismiss, displace, double for, eject, exchange, expel, fill in for,
   force out, ghost, ghostwrite, oust, pinch-hit, relieve, remove,
   replace, represent, spell, spell off, stand in for, step,
   subrogate, substitute, substitute for, succeed, supersede,
   swap places with, turn out, understudy for, unseat, usurp