From WordNet (r) 2.0 (August 2003) [wn]:
outhouse
n : a small outbuilding with a bench having holes through which
a user can defecate [syn: privy, earth-closet,
jakes]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]