The Collaborative International Dictionary of English v.0.48:

Gatehouse \Gate"house`\ (g[=a]t"hous`), n.
   A house connected or associated with a gate.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gatehouse
    n 1: a house built at a gateway; usually the gatekeeper's
         residence

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "gatehouse":
   Nissen hut, Quonset hut, booth, crib, hut, hutch, kiosk, lean-to,
   outbuilding, outhouse, pavilion, sentry box, shack, shanty, shed,
   stall, tollbooth, tollhouse