The Collaborative International Dictionary of English v.0.48:

Brothel \Broth"el\, n. [OE. brothel, brodel, brethel, a
   prostitute, a worthless fellow, fr. AS. ber['o][eth]an to
   ruin, destroy; cf. AS. bre['o]tan to break, and E. brittle.
   The term brothel house was confused with bordel brothel. CF.
   Bordel.]
   A house of lewdness or ill fame; a house frequented by
   prostitutes; a bawdyhouse.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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