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)