The Collaborative International Dictionary of English v.0.48:

Unsting \Un*sting"\, v. t. [1st pref. un- + sting.]
   To disarm of a sting; to remove the sting of. [R.] "Elegant
   dissertations on virtue and vice . . . will not unsting
   calamity." --J. M. Mason.
   [1913 Webster]