The Collaborative International Dictionary of English v.0.48:

Evanish \E*van"ish\, v. i. [Pref. e- + vanish: cf. L.
   evanescere. See Evanesce, vanish.]
   To vanish.
   [1913 Webster]

         Or like the rainbow's lovely form,
         Evanishing amid the storm.               --Burns.
   [1913 Webster]