geothermal
adj.relating to the heat that comes from inside the earth. You usually hear this word when people talk about clean energy or hot springs.
adj.relating to or produced by the internal heat of the earth. Often describes energy sources or geological features like geysers and hot springs.
“The city uses geothermal energy to heat homes.”
“Iceland produces a significant portion of its electricity by tapping into geothermal reservoirs deep underground.”
“Engineers are exploring enhanced geothermal systems that could potentially harness heat from dry rock layers, significantly expanding the geographic availability of this renewable resource.”
Typically used attributively before a noun like 'energy', 'power', or 'heating'.
“The proposed facility was to run on geothermal energy and eventually scale to as much as 1 gigawatt of capacity.”
“It poses no immediate danger, but the discovery reveals how enormous volcanic systems can remain hidden and could transform the search for geothermal energy and critical minerals.”
From geo- + thermal.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.