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):

supplanting
    n 1: act of taking the place of another especially using
         underhanded tactics [syn: supplanting, displacement]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "supplanting":
   agency, change, commutation, delegation, deputation, deputyship,
   displacement, exchange, power of attorney, quid pro quo,
   replacement, representation, subrogation, substitution,
   supersedence, superseding, supersedure, supersession,
   supplantation, supplantment, switch, tit for tat, vicariousness