The Collaborative International Dictionary of English v.0.48:

Bordel \Bor"del\, Bordello \Bor*del"lo\, n. [F. bordel, orig. a
   little hut, OF. borde hut, cabin, of German origin, and akin
   to E. board,n.See. Board, n.]
   A brothel; a bawdyhouse; a house devoted to prostitution.
   [Obs.] --B. Jonson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bordello \Bor"del*lo\, n.
   a building where prostitutes are available for hire; a
   brothel.

   Syn: whorehouse, whore house, brothel, bagnio, house of
        prostitution, house of ill repute, bawdyhouse, bawdy
        house, cathouse, sporting house.
        [PJC + WordNet 1.5]

WordNet (r) 3.0 (2006):

bordello
    n 1: a building where prostitutes are available [syn:
         whorehouse, brothel, bordello, bagnio, house of
         prostitution, house of ill repute, bawdyhouse,
         cathouse, sporting house]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "bordello":
   bagnio, bawdy house, bawdyhouse, brothel, cathouse, clip joint,
   crib, den, den of thieves, den of vice, disorderly house, dive,
   dump, fleshpots, gyp joint, hole, house of assignation,
   house of joy, house of prostitution, joint, lair, panel den,
   panel house, red-light district, sink of iniquity, sporting house,
   stew, stews, tenderloin, whorehouse