gatehouse

< /ˈgeɪtˌhaʊ zɪz/.

1. a house at or over a gate, used as a gatekeeper’s quarters, fortification, etc.
2. a house or structure at the gate of a dam, reservoir, etc., with equipment or controls for regulating the flow of water.

noun

1. a building above or beside an entrance gate to a city, university, etc, often housing a porter or guard, or (formerly) used as a fortification
2. a small house at the entrance to the grounds of a country mansion
3. a structure that houses the controls operating lock gates or dam sluices