Meaning of hydrothermal

hy•dro•ther•mal

Pronunciation: (hī"dru-thûr'mul), [key]
— adj. Geol.
  1. noting or pertaining to the action of hot, aqueous solutions or gases within or on the surface of the earth.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.