1. A reference to heated water, to its action, or to the products of such action.
2. Applied to the action of heated water in bringing about changes in the earth's crust.
3. A reference to hot water on or beneath the surface of the earth.
4. Relating to hot water, especially to naturally occurring hot water in thermal springs.
5. Relating to or caused by heated water; especially, the action of water heated by natural processes rather than by industrial activity.