The Collaborative International Dictionary of English v.0.48:

Extirpate \Ex"tir*pate\ (?; 277), v. t. [imp. & p. p.
   Extirpated; p. pr. & vb. n. Extirpating.] [L. extirpatus,
   exstirpatus, p. p. of extirpare, exstirpare; ex out + strips
   stock, stem, root.]
   To pluck up by the stem or root; to root out; to eradicate,
   literally or figuratively; to destroy wholly; as, to
   extirpate weeds; to extirpate a tumor; to extirpate a sect;
   to extirpate error or heresy.

   Syn: To eradicate; root out; destroy; exterminate;
        annihilate; extinguish.
        [1913 Webster]

WordNet (r) 3.0 (2006):

extirpate
    v 1: destroy completely, as if down to the roots; "the vestiges
         of political democracy were soon uprooted" "root out
         corruption" [syn: uproot, eradicate, extirpate, root
         out, exterminate]
    2: pull up by or as if by the roots; "uproot the vine that has
       spread all over the garden" [syn: uproot, extirpate,
       deracinate, root out]
    3: surgically remove (an organ)

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "extirpate":
   abate, abolish, abscind, amputate, annihilate, ban, bar, blot, bob,
   clip, crop, cull, cut, cut away, cut off, cut out, deracinate,
   dock, eliminate, enucleate, eradicate, except, excise, exclude,
   exterminate, extinguish, isolate, knock off, liquidate, lop,
   mutilate, nip, pare, peel, pick out, prune, purge, remove,
   root out, root up, rule out, set apart, set aside, shave, shear,
   stamp out, strike off, strip, strip off, sweep away, take off,
   take out, truncate, uproot, wipe out