1875, from geo- + thermal.

/ˌʤiːjoʊˈθɚməl/ adjective geothermal /ˌʤiːjoʊˈθɚməl/ adjective Learner's definition of GEOTHERMAL : of, relating to, or using the natural heat produced inside the Earth geothermal power [..]

Power generated from heat energy derived from hot rock, hot water, or steam below the earth's surface.

heat from within the earth. By pumping water down to hot rock layers where magma is close to the surface, we can use the resultant steam to drive turbines and produce electricity. On a smaller scale t [..]

Relating to or created by the internal heat of the Earth.

Geothermal energy is heat from within the earth. We can use the steam and hot water produced inside the earth to heat buildings or generate electricity. Geothermal energy is a renewable energy source because the water is replenished by rainfall and the heat is continuously produced inside the earth. Source: U.S. Department of Energy

relating to [1] natural heat within the crust; [2] heat from hot groundwater or steam used for power generation

For the most part, geothermal relates to geothermal electricity production, but there are several articles related to geothermal heat pumps.

(adj) of or relating to the heat in the interior of the earth

Of, relating to, or produced by the internal heat of the Earth. Our geothermal technology services offer your commercial and residential projects cost-­‐effective and environmentally responsible solutions.

typically a base load form of generation. Where natural ground heating occurs – often in volcanic areas of the world such as the Pacific Rim – the ground heat can be captured and converted into electricity.

Describes the technology used to tap subsurface heat to produce energy. Low-temperature geothermal energy at very shallow, shallow and medium depths is used to heat homes, public buildings and office [..]

is pertaining to heat energy extracted from reservoirs in the earth's interior, as is the use of geysers, molten rock and steam spouts. Geothermal energy is the heat generated by natural processe [..]

Pertains to the heat of the Earth's interior. Grab sample

Heat energy from inside the Earth.

Geothermal systems use the solar energy that is stored year-round just beneath the earth's surface. This energy is free, unlimited, 100% renewable. A geothermal system is a proven cost-effecti [..]

Power generated from heat energy derived from hot rock, hot water or steam below the earth's surface.

Pertaining to the heat of the interior of the Earth.

Concerning heat flowing from deep in the earth

energy - energy derived from the natural heat of the earth contained in hot rocks, hot water, hot brine or steam.

A heating source that is produced from the internal heat of the earth. For example ground source heat pumps.