The Collaborative International Dictionary of English v.0.48:

Unmake \Un*make"\, v. t. [1st pref. un- + make.]
   To destroy the form and qualities of; to deprive of being; to
   uncreate.
   [1913 Webster]

         God does not make or unmake things to try experiments.
                                                  --T. Burnet.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unmake
    v 1: deprive of certain characteristics [syn: unmake, undo]
         [ant: do, make]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "unmake":
   atomize, break to pieces, cleave, decimate, demolish, dethrone,
   disassemble, discrown, disenthrone, disintegrate, dismantle,
   displace, fragment, make mincemeat of, pick to pieces,
   pull in pieces, pull to pieces, pulverize, raze, reduce to rubble,
   rend, ruin, shatter, smash, split, sunder, take apart, tear apart,
   tear to pieces, tear to shreds, tear to tatters, total, unbuild,
   uncrown, undo, wrack, wrack up, wreck