The Collaborative International Dictionary of English v.0.48:

outhouse \out"house`\, n.
   1. A small house or building at a little distance from the
      main house; an outbuilding.
      [1913 Webster]

   2. Especially: A small building with one or more seats and a
      pit underneath, intended for use as a toilet; a privy.
      [PJC]

WordNet (r) 3.0 (2006):

outhouse
    n 1: a small outbuilding with a bench having holes through which
         a user can defecate [syn: outhouse, privy, earth-
         closet, jakes]