The Collaborative International Dictionary of English v.0.48:

Ungowned \Un*gowned"\, a.
   1. [1st pref. un- + gown.] Stripped of a gown; unfrocked.
      [1913 Webster]

   2. [Pref. un- not + gowned.] Not having, or not wearing, a
      gown.
      [1913 Webster]