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geothermal

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Etymology and origin of the English word geothermal

Confidence
Established
Formation
Compound
First attested
1830 Edinburgh Journal of Science
Ultimate origin
Ancient Greek γῆ,θέρμη
Etymology tree
inherited borrowed derived
English thermal
English geothermal

Pronunciation

  • UK: /ˌdʒiːəʊˈθɜːm(ə)l/, /ˌdʒiːəˈθɜːm(ə)l/[1]
  • US: /ˌdʒiːoʊˈθɝːm(ə)l/, /ˌdʒiːəˈθɝːm(ə)l/[1]

Etymology

It is formed from English geo- + thermal;[2][3][4][5] Merriam-Webster classes it as International Scientific Vocabulary, from geo- and thermal or thermic.[6] The prefix comes from Ancient Greek γῆ (gê, “the earth, land”),[3] and thermal comes through French thermal from θέρμη (thérmē, “heat, feverish heat”).[3] In the horticultural sense the word followed French géothermique (1861).[2]

Earliest recorded meaning

Relating to or caused by the internal heat of the earth: 1830, in the Edinburgh Journal of Science.[2] Etymonline dates the word to 1858 and its synonym geothermic to 1859;[3] Merriam-Webster gives 1875 and Dictionary.com 1870–75.[6][5]

Semantic evolution

A short-lived horticultural sense, of growing plants in heated soil, is recorded only from 1861 to 1879, after the French.[2] The sense of energy or power for human use, drawn from the heat of the earth's crust, appeared in 1927.[2] As a noun the word meant a line joining points of equal temperature below ground (an isogeotherm), from 1895 in the OED and by 1909 in Etymonline;[2][3] later it was used of hot springs, geysers and similar features (1957) and of geothermal energy itself (1960).[2]

Timeline

  • 1830 – relating to the internal heat of the earth.[2]
  • 1861 – in horticulture, of heated soil (obsolete by 1879).[2]
  • 1895 – noun, a line of equal underground temperature.[2] Etymonline dates the noun to 1909.[3]
  • 1927 – of energy or power, drawn from the earth's heat.[2]
  • 1957 – noun, a hot spring, geyser or similar feature.[2]
  • 1960 – noun, geothermal energy.[2]

Meanings

Adjective

  1. Relating to or produced by the heat of the earth's interior: geothermal springs.[7][6][2]
  2. Of energy or power, obtained from the heat of the earth's interior, or relating to its production: a geothermal power station.[2][6]

Noun

  1. Geothermal energy.[2]
  2. A feature such as a hot spring, geyser or fumarole, heated from below; usually in the plural.[2]

Word family

  • geothermally

Usage notes

Geothermic is used in the same sense.[7][6][4]

References

  1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
  2. ^ a b c d e f g h i j k l m n o p q Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
  3. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
  4. ^ a b Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
  5. ^ a b Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
  6. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
  7. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins
Cite this entry

“Geothermal.” Etymologically, 1 Nov. 2026, etymologically.com/en/geothermal. Accessed 2 Nov. 2026.

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