Source : Webster's Revised Unabridged Dictionary (1913)

Dehorn \De*horn"\, v. t. [imp. & p. p. {Dehorned}; p. pr. & vb.
   n. {Dehorning}.]
   To deprive of horns; to prevent the growth of the horns of
   (cattle) by burning their ends soon after they start. See
   {Dishorn}. ``Dehorning cattle.'' --Farm Journal (1886).

Source : WordNet®

dehorn
     v 1: prevent the growth of horns of certain animals
     2: take the horns off (an animal)