The Collaborative International Dictionary of English v.0.48:

Ungod \Un*god"\, v. t. [1st pref. un- + god.]
   1. To deprive of divinity; to undeify. [R.] --Donne.
      [1913 Webster]

   2. To cause to recognize no god; to deprive of a god; to make
      atheistical. [R.] --Dryden.
      [1913 Webster]