having to do with hot water; esp., having to do with the action of hot water in producing minerals and springs or in dissolving, shifting, and otherwise changing the distribution of minerals in the earth's crust
See hydrothermal in American Heritage Dictionary 4
Of or relating to hot water.
a. Of or relating to hot magmatic emanations rich in water.
b. Of or relating to the rocks, ore deposits, and springs produced by such emanations.