: of, relating to, or utilizing the heat of the earth's interior
also : produced or permeated by such heat
geothermal steam
geothermal regions

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Geothermal comes partly from the Greek thermos, "hot". Most geothermal electricity is provided by power plants situated in areas where there is significant activity of the Earth's great tectonic plates—often the same areas where volcanoes are found. But hot water from deep underground may be used by cities far from volcanoes to heat buildings or sidewalks. And a newer source of geothermal energy relies on a less dramatic kind of heat: Individual homeowners can now install heat pumps that take advantage of the 50°-60° temperature of the soil near the surface to provide heating in cold weather (and air-conditioning in the warm months). These very small-scale geothermal systems may eventually supply more useful energy than the large power plants.

Examples of geothermal in a Sentence

Recent Examples on the Web
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Houses are bio-climate smart, using cutting-edge solar and geothermal energy sources. Condé Nast, Condé Nast Traveler, 21 Aug. 2026 That would include 2,000 MW of nuclear power alongside 700 MW of hydropower and new geothermal projects. ABC News, 19 Aug. 2026 The university also says this complex is all-electric, supported by on-site solar panels and geothermal heating and cooling. Jack Springgate, CBS News, 19 Aug. 2026 The geothermal water was first used by Indigenous peoples, and holes ground into limestone rock remain as archeological proof of their hot spring use. Evie Carrick, Travel + Leisure, 18 Aug. 2026 See All Example Sentences for geothermal

Word History

Etymology

geo- + thermal entry 1

First Known Use

1875, in the meaning defined above

Time Traveler
The first known use of geothermal was in 1875

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Cite this Entry

“Geothermal.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/geothermal. Accessed 26 Aug. 2026.

Kids Definition

geothermal

adjective
variants also geothermic
-mik
: of, relating to, or using the heat of the earth's interior
also : produced by such heat
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