water lock
/ˈwɔːtə lɒk/noun
1On a river, canal, etc.: = lock 11a. Now rare.
- Recorded earliest in a surname..
2Any of various devices or contrivances for locking water into or out of something, or in which water is used to seal something off.
3An airlock for use underwater.
Origin
Middle English; earliest use found in Close Rolls Henry III. From water + lock.