Floodgate and Lock-gate

Floodgate noun - Regulator consisting of a valve or gate that controls the rate of water flow through a sluice.

Lock-gate and floodgate are semantically related. In some cases you can use "Lock-gate" instead a noun "Floodgate".

Lock-gate noun - A gate that can be locked.

Floodgate and lock-gate are semantically related. You can use "Floodgate" instead a noun phrase "Lock-gate".