gatehouse

Short definition from Wiktionary

Noun

1. 1
   A lodge besides the entrance to an estate; often the residence of a gatekeeper; also a dwelling formerly used as such a residence.
2. 2
   A fortified room over the entrance to a castle or over the gate in a city wall
3. 3
   A shelter for a gatekeeper.

Proper noun

1. 1
   A surname.