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

Other Words from thermal


thermally \ ˈthər-​mə-​lē How to pronounce thermal (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 Horvath worked with data from a thermal camera on NASA’s Lunar Reconnaissance Orbiter, which didn’t yield too much information. Marina Koren, The Atlantic, 29 July 2022 The number of technologies targeted for tax breaks is dizzying: fuel cells, geothermal, energy storage, biogas, microgrids, thermal energy storage, hydrogen production, tint-changing windows, roof insulation, and more are all singled out. John Timmer, Ars Technica, 28 July 2022 Now, new research suggests the pits' thermal environment is more hospitable than anywhere else on the Moon, with temps hovering around 63℉ (17℃). Stephanie Mlot, PCMAG, 27 July 2022 Chun explains that compared to older thermal technologies, this one leads to less downtime. Jamie Wilson, Harper's BAZAAR, 25 July 2022 Russia’s artillery attacks also hit a thermal power plant in Donetsk Oblast, causing a fire on its territory. Katya Soldak, Forbes, 12 June 2022 On April 26, Russian troops fired rockets into the Kryvorizka thermal power plant in the Dnipropetrovsk region. Vivienne Walt, Fortune, 31 May 2022 An employee works on a gas installation at the Sofia Iztok thermal power plant on May 5, 2022, a week after the halt of Russian gas supply to Bulgaria. Patrick Smith, NBC News, 7 May 2022 Russian military forces also have appeared to prioritize critical infrastructure, using air power to target a thermal power plant near Kyiv, Ukrainian officials said. Washington Post, 24 Feb. 2022 Recent Examples on the Web: Noun With lockdowns lifting, many employers plan to use systems, including fever-detecting thermal cameras, mask-checking systems and corporate contact-tracing devices, to help prevent new Covid-19 outbreaks. Stephanie Bodoni,, 1 June 2020 Fever-checking thermal cameras are also starting to become ubiquitous. Helene Fouquet, Fortune, 23 May 2020 Fever-checking thermal cameras are also starting to become ubiquitous. Helene Fouquet, Fortune, 23 May 2020 Fever-checking thermal cameras are also starting to become ubiquitous. Helene Fouquet,, 20 May 2020 Some airports, such as London Heathrow, Puerto Rico's San Juan airport, and Paine Field—a secondary airport in Seattle—are using thermal cameras to scan crowds for feverish temperatures. Jessica Puckett, Condé Nast Traveler, 12 May 2020 In Florida's Palm Beach County, Dahua thermal cameras sold by RedSpeed and installed last month scan everyone who enters the county jail and courthouse, while a deputy with a laptop reviews people's temperatures from nearby. Drew Harwell, Anchorage Daily News, 11 May 2020 In Midtown Manhattan, thermal cameras will measure body temperatures as employees file into a 32-story office tower at Rockefeller Center. Konrad Putzier And Chip Cutter, WSJ, 5 May 2020 More than 1,500 thermal cameras were shipped to Amazon warehouses by China’s Zhejiang Dahua Technology, and at least 500 of the cameras are being sold within the U.S., Reuters reported Wednesday citing three sources. Spencer Neale, Washington Examiner, 29 Apr. 2020 See More

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.

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

Learn More About thermal

Time Traveler for thermal

Time Traveler

The first known use of thermal was in 1742

See more words from the same year

Dictionary Entries Near thermal

Thermaïkós Kólpos


thermal agitation

See More Nearby Entries 

Statistics for thermal

Last Updated

6 Aug 2022

Cite this Entry

“Thermal.” Dictionary, Merriam-Webster, Accessed 15 Aug. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

More Definitions for thermal


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 thermal (audio) \ adverb

More from Merriam-Webster on thermal

Nglish: Translation of thermal for Spanish Speakers

Britannica English: Translation of thermal for Arabic Speakers


Test Your Vocabulary

Commonly Confused Words Quiz

  • vector image of a face with thought expression
  • I went to the ______ store to buy a birthday card.
Spell It

Can you spell these 10 commonly misspelled words?

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!