The Collaborative International Dictionary of English v.0.48:

Bruiser \Bruis"er\, n.
   1. One who, or that which, bruises.
      [1913 Webster]

   2. A boxer; a pugilist; hence, a strong, tough person; --
      often used in the phrase

   big bruiser. --R. Browning.
      [1913 Webster]

            Like a new bruiser on Broughtonic sand,
            Amid the lists our hero takes his stand. --T.
                                                  Warton.
      [1913 Webster]

   3. A concave tool used in grinding lenses or the speculums of
      telescopes. --Knight.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bruiser
    n 1: a large and strong and heavyset man; "he was a bull of a
         man"; "a thick-skinned bruiser ready to give as good as he
         got" [syn: bull, bruiser, strapper, Samson]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "bruiser":
   Chinese boxer, bantamweight, black belt, bodyguard, bouncer, boxer,
   brown belt, enforcer, featherweight, fighter, fisticuffer,
   flyweight, goon, gorilla, gun, gunsel, hatchet man, heavyweight,
   hellion, holy terror, hood, hoodlum, hooligan, karate expert,
   light heavyweight, lightweight, middleweight, mug, mugger,
   muscle man, palooka, plug-ugly, prizefighter, pug, pugilist,
   rodman, roughneck, ruffian, savate expert, sparrer, strong-arm man,
   terror, thug, torpedo, tough, tough guy, trigger man,
   ugly customer, welterweight