water hammer

(Physics) 1. A vessel partly filled with water, exhausted of air, and hermetically sealed. When reversed or shaken, the water being unimpeded by air, strikes the sides in solid mass with a sound like that of a hammer. [ 1913 Webster ]

2. A concussion, or blow, made by water in striking, as against the sides of a pipe or vessel containing it. [ 1913 Webster ]

3. A metal hammer used when heated, as by dipping in hot water, to blister the skin, as for counterritation. [ Webster 1913 Suppl. ]