Source : Webster's Revised Unabridged Dictionary (1913)

Boorish \Boor"ish\, a.
   Like a boor; clownish; uncultured; unmannerly. --
   {Boor"ish*ly}, adv. -- {Boor"ish*ness}, n.

         Which is in truth a gross and boorish opinion.
                                                  --Milton.

Source : WordNet®

boorishly
     adv : like a boor, "he behaved boorishly at the party"