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]
A concussion, or blow, made by water in striking, as against the sides of a pipe or vessel containing it. [1913 Webster]
A metal hammer used when heated, as by dipping in hot water, to blister the skin, as for counterritation. [Webster 1913 Suppl.]

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