VERB (3)

1. add nonfissionable material to (fissionable material) so as to make unsuitable for use in an atomic bomb;

2. modify (as a native protein) especially by heat, acid, alkali, or ultraviolet radiation so that all of the original properties are removed or diminished;

3. make (alcohol) unfit for drinking without impairing usefulness for other purposes;

The Collaborative International Dictionary of English v.0.48:

Denature \De*na"ture\, v. i.
   To become denatured.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Denature \De*na"ture\, v. t. [De- + nature.]
   To deprive of its natural qualities; change the nature of.
   [Webster 1913 Suppl.]

   2. to render (ethyl alcohol) unfit to drink by adding in
      toxic or unpalatable substances (such as benzene or
      pyridine) which nevertherless permit alcohol to be used as
      a solvent.
      [PJC]

   3. modify the tertiary structure of (a protein or nucleic
      acid) so as to reduce or destroy its characteristic
      biological activity.

   Note: Bioactive macromolecules such as enzymes or DNA may be
         denatured by heat, acid, alkali, or solvent treatment;
         the extent of such treatment required to denature a
         molecule varies with the specific compound. In some
         cases the denatured molecules may regain their original
         properties (renature) by other treatments. Denaturation
         may also cause a change in the physical properties of
         such molecules, e.g. proteins may become insoluble in
         water.
         [PJC]

WordNet (r) 3.0 (2006):

denature
    v 1: add nonfissionable material to (fissionable material) so as
         to make unsuitable for use in an atomic bomb
    2: modify (as a native protein) especially by heat, acid,
       alkali, or ultraviolet radiation so that all of the original
       properties are removed or diminished
    3: make (alcohol) unfit for drinking without impairing
       usefulness for other purposes