The Collaborative International Dictionary of English v.0.48:

defuse \de*fuse"\ (d[-e]*f[=u]z"), v. t. [Cf. Diffuse.]
   1. To disorder; to make shapeless. [Obs.] --Shak.
      [1913 Webster]

   2. To remove the fuse from; to deactivate (a bomb or other
      explosive device) or make it ineffective.

   Syn: deactivate.
        [WordNet 1.5 +PJC]

   3. To make less dangerous; as, to defuse a tense
      confrontation between demonstrators and police.
      [PJC]

WordNet (r) 3.0 (2006):

defuse
    v 1: remove the triggering device from [ant: fuse]