geo·​ther·​mal ˌjē-ō-ˈthər-məl How to pronounce geothermal (audio)
: of, relating to, or utilizing the heat of the earth's interior
also : produced or permeated by such heat
geothermal steam
geothermal regions
geothermally adverb

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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 Aftershocks are not to be confused with swarms, which are sequences of small earthquakes associated with geothermal activity with no identifiable mainshock. Clare Mulroy, USA TODAY, 5 Apr. 2024 But a grid-less future doesn’t have to involve every homeowner installing solar panels or drilling for geothermal power. Eric MacK, Forbes, 28 Mar. 2024 But air conditioning is eschewed here in favor of a geothermal cooling system — waiting to be tested against the city’s increasingly frequent summer heat waves. Alexander Smith, NBC News, 26 Mar. 2024 Compared to geothermal, air-source models use more power, have a lifespan of around 15 years, and lose some efficiency in very cold weather. Tik Root, WIRED, 30 Mar. 2024 The upper 10 kilometers of the Earth’s crust contains vast geothermal reserves, essentially awaiting human energy consumption to begin to tap into its unstinting power output—which itself yields no greenhouse gasses. IEEE Spectrum, 29 Mar. 2024 The eruptions near Grindavík over the last six months have continued to threaten the town, the Blue Lagoon and the geothermal plant on the Reykjanes Peninsula. Erik Klemetti, Discover Magazine, 27 Mar. 2024 The nearby geothermal spa Blue Lagoon was also evacuated, Olafsson said on social media. Meredith Deliso, ABC News, 16 Mar. 2024 Bukele has also sketched plans for a tax-free crypto haven powered by geothermal energy from a volcano. Reuters, NBC News, 15 Mar. 2024

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'geothermal.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


geo- + thermal entry 1

First Known Use

1875, in the meaning defined above

Time Traveler
The first known use of geothermal was in 1875

Dictionary Entries Near geothermal

Cite this Entry

“Geothermal.” Dictionary, Merriam-Webster, Accessed 22 Apr. 2024.

Kids Definition


geo·​ther·​mal ˌjē-ō-ˈthər-məl How to pronounce geothermal (audio)
variants also geothermic
: of, relating to, or using the heat of the earth's interior
also : produced by such heat
Last Updated: - Updated example sentences
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