ther·​mal | \ ˈthər-məl How to pronounce thermal (audio) \

Definition of thermal

 (Entry 1 of 2)

1a : of, relating to, or caused by heat thermal stress thermal insulation
b : being or involving a state of matter dependent upon temperature thermal conductivity thermal agitation of molecular structure
c : having low energies of the order of those due to thermal agitation thermal neutrons
2 : designed (as with insulating air spaces) to prevent the dissipation of body heat thermal underwear
3 [ Latin thermae public baths, from Greek thermai, plural of thermē ] : of, relating to, or marked by the presence of hot springs thermal waters



Definition of thermal (Entry 2 of 2)

: a rising body of warm air

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Other Words from thermal


thermally \ ˈthər-​mə-​lē How to pronounce thermally (audio) \ adverb

Did You Know?

In days gone by, much of the male population of the northern states in the cold months would wear a garment of thermal underwear covering the entire body, called a union suit. Union suits kept sodbusters, cowboys, and townsfolk alike not only warm but also itchy and a little on the smelly side (back when bathing once a week was considered the height of cleanliness). Thermal imaging is photography that captures "heat pictures"--rather than ordinary light pictures--of objects. And thermal pollution occurs when industrial water use ends up warming a river in a damaging way. Small-plane pilots use thermal as a noun for a warm updraft, often over a plowed field or desert, that lifts their wings, just as it enables hawks to soar upward without moving their wings.

Examples of thermal in a Sentence

Recent Examples on the Web: Adjective

For example, one of these impacts is a phenomenon called thermal expansion. Jennifer Leman, Popular Mechanics, "What Is Methane, Anyway?," 29 Aug. 2019 In bathtub water-level terms, the melting of continental ice sheets is to thermal expansion as a rubber duck is to a person. The Economist, "Climate change is a remorseless threat to the world’s coasts," 17 Aug. 2019 In 2015, the government of prime minister Narendra Modi launched new standards to limit the concentration of pollutants from the stack emissions of thermal power plants. Kuwar Singh, Quartz India, "Cleaning up its coal power plants will cost India $10 billion—but who will pay?," 7 Aug. 2019 Economy, Trade and Industry Minister Hiroshige Seko told reporters that the extensive power outage was caused by an emergency shutdown of the main thermal power plant at Tomato Atsuma that supplies half of Hokkaido's electricity. Fox News, "At least 7 dead, dozens feared buried after quake hits northern Japan," 2 Oct. 2018 The rifle was paired with a helmet whose eyepiece showed, with night vision and thermal vision, where the rifle was pointed as well as what was directly in front of the soldier. Sabrina Schnur,, "US Army researchers in Natick display new technology at the State House," 19 June 2019 Other system additions include networked thermal cameras installed along the reserve's perimeter and fiber-optic acoustic sensors. Sean Gallagher, Ars Technica, "We know you hate the Internet of Things, but it’s saving megafauna from poachers," 6 June 2018 Ray Radakovich, of the Greenfield Police Department, said his agency purchased the thermal-vision drone four months ago. Elliot Hughes, Milwaukee Journal Sentinel, "Spike strip, K-9, drone used to apprehend fleeing suspect in Greenfield," 12 Apr. 2018 In a press release, Shine says that the Goldilocks Zone may be turtles’ defense against thermal conditions linked with shifting temperatures. Meilan Solly, Smithsonian, "Turtle Embryos May Be Able to Influence Their Sex by Moving Around Inside the Egg," 2 Aug. 2019

Recent Examples on the Web: Noun

The chip is rated to dissipate up to 15 watts of thermals and has a base clock of 2.3GHz and 4GHz boost frequencies. Gordon Mah Ung, PCWorld, "Lenovo puts AMD Ryzen chips in ThinkPads, giving Intel's rival a boost," 8 May 2019 Aviators can't use autopilot in trying conditions that can range from thermals rising out of flaming forests to flying low through mountain ranges. Meg Jones, Milwaukee Journal Sentinel, "Firefighting planes and their crews spotlighted at EAA AirVenture," 27 July 2019 Buy Now: Tangle Teezer Hairbrush, $7.60 (originally $12) Olaplex Hair Perfector No. 3 Treatment Created by two chemistry PhDs, this reparative hair treatment relinks hair bonds broken by chemical, thermal, and mechanical processes. Cnt Editors, Condé Nast Traveler, "The Best Amazon Prime Day Beauty Deals for Frequent Travelers," 16 July 2019 After all these years, the world’s very first national park is still one of its most imposing, a blend of land and water, forest and field, wildlife and geo-thermal features that often seem to be living things. Dan Westergren, National Geographic, "Yellowstone National Park," 12 Apr. 2019 Turkey vultures circled overhead, riding the thermals against a backdrop of bright blue Colorado sky. Sarah Kuta, The Know, "What are via ferratas and why is Colorado so crazy about them?," 2 July 2019 The parents are showing them how to survive, how to find food, how to navigate thermals. San Diego Union-Tribune, "Column: Why the Safari Park’s California condor dads are Father’s Day stars," 14 June 2019 That alone is big news, but there are other welcome improvements with this generation, from display and color choices to thermals. Melissa Riofrio, PCWorld, "Finally! The new Dell XPS 13 puts the camera in the right place," 8 Jan. 2019 Take thermals, columns of rising air that form when the ground below warms through sunlight. David Grossman, Popular Mechanics, "Vultures Use Social Networks to Share Crucial Flight Information," 8 Nov. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'thermal.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of thermal


1742, in the meaning defined at sense 3


1933, in the meaning defined above

History and Etymology for thermal


Greek thermē

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Statistics for thermal

Last Updated

3 Sep 2019

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Time Traveler for thermal

The first known use of thermal was in 1742

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English Language Learners Definition of thermal

 (Entry 1 of 2)

: of, relating to, or caused by heat
: designed to keep you warm by preventing heat from leaving your body
: having hot water flowing out of the ground



English Language Learners Definition of thermal (Entry 2 of 2)

: a rising current of warm air that is produced when the sun heats an area of the ground
British : thermal clothing or underwear


ther·​mal | \ ˈthər-məl How to pronounce thermal (audio) \

Kids Definition of thermal

: of, relating to, or caused by heat thermal insulation


ther·​mal | \ ˈthər-məl How to pronounce thermal (audio) \

Medical Definition of thermal

1 : of, relating to, or caused by heat tactile and thermal senses
2 : being or involving a state of matter dependent upon temperature thermal agitation of molecular structure

Other Words from thermal

thermally \ -​mə-​lē How to pronounce thermally (audio) \ adverb

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More from Merriam-Webster on thermal

Rhyming Dictionary: Words that rhyme with thermal

Spanish Central: Translation of thermal

Nglish: Translation of thermal for Spanish Speakers

Britannica English: Translation of thermal for Arabic Speakers

Comments on thermal

What made you want to look up thermal? Please tell us where you read or heard it (including the quote, if possible).


agony, or difficult or painful work

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