The Collaborative International Dictionary of English v.0.48:

Brutish \Bru"tish\, a.
   Pertaining to, or resembling, a brute or brutes; of a cruel,
   gross, and stupid nature; coarse; unfeeling; unintelligent.
   [1913 Webster]

         O, let all provocation
         Take every brutish shape it can devise.  --Leigh Hunt.
   [1913 Webster]

         Man may . . . render himself brutish, but it is in vain
         that he would seek to take the rank and density of the
         brute.                                   --I. Taylor.
   [1913 Webster]

   Syn: Insensible; stupid; unfeeling; savage; cruel; brutal;
        barbarous; inhuman; ferocious; gross; carnal; sensual;
        bestial.
        [1913 Webster] -- Bru"tish*ly, adv. --
        Bru"tish*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

brutishly
    adv 1: in an inhumane manner; "she treated her husband
           bestially" [syn: bestially, brutishly, in a beastly
           manner]