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

Among several features, the enhancements include an estimated flight time of 31 minutes, a spotlight, a speaker system and infrared and thermal sensors. Mark Puente,, "LAPD wants to make drone program permanent and expand uses for the aerial devices," 5 July 2019 Instead of getting thermal energy from electricity or a direct flame, pavement relies on the absorption of light from the sun. Emily Toomey, Smithsonian, "Attempting to Fry an Egg on the Sidewalk Has Been a Summer Pastime for Over 100 Years," 4 July 2019 The curtains have thermal and blackout linings to keep things toasty and private for sleeping, and they can be tied back or removed altogether when not needed; the skylight has a screen to let in fresh air while keeping bugs away. Michele Petry, House Beautiful, "How Newlyweds Turned a Van into the Cutest Tiny Home Ever," 2 July 2019 There are two types of desalination—thermal, which heats up water and then captures the condensation, and reverse osmosis, which forces sea water through the pores of a membrane that are many times smaller than the diameter of a human hair. Jim Robbins, WIRED, "Desalination Is Booming as Cities Run out of Water," 27 June 2019 The mobile unit has daylight and thermal capabilities, can withstand winds up to 70 or 75 mph, and can run for seven days straight without refueling. Carol Robinson |,, "Homewood police deploy ‘eye in the sky’ to help fight crime," 26 June 2019 Those nascent internet days also featured clever hoarding of thermal fax paper (!) and manning the lone Datebook email for at least 25 full-time writers, columnists and critics. Catherine Bigelow,, "SF Chronicle columnist Leah Garchik gets a big thank you and swell sendoff," 25 June 2019 The Argentine government has commissioned more hydroelectric, thermal and renewable energy projects, as well as a modernization of the transmission system, which is highly regulated. New York Times, "‘Massive Failure’ in Power Grid Causes Blackout in Argentina and Uruguay," 16 June 2019 It is also expected to provide dynamic thermal and visible camouflage options. Allison Barrie, Fox News, "New futuristic Israeli 'dune-buggy' is bristling with weapons, ready for combat," 22 June 2018

Recent Examples on the Web: Noun

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 Matek is a new base-layer brand built for the slopes, but its thermals are chic enough to wear on their own with a skirt or jeans. Anny Choi, Vogue, "5 Cold-Weather Styling Tricks You Can Take to the Office," 19 Jan. 2019 The turbo boosting should also be smarter, able to push the processor closer to its thermal and power limits. Peter Bright, Ars Technica, "Second-generation Threadripper goes on sale: $1,799 for 32 cores," 6 Aug. 2018 Feel the heat Solar thermal revolves around transfers of heat. John Timmer, Ars Technica, "New material could up efficiency of concentrated solar power," 19 Oct. 2018 The raptor will tell you where the thermals — the uplifting air currents — are. Alan Berner, The Seattle Times, "Go, hawks: Sailplane pilots look to birds for flying tips," 23 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

9 Jul 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

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