ther·​mal | \ ˈthər-məl \

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

Keep scrolling for more

Other Words from thermal


thermally \ ˈthər-​mə-​lē \ 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

Begin by prepping with a thermal protectant spray like TRESemmé Thermal Creations Heat Tamer Spray ($6). Jaime Osnato, SELF, "10 Styling Hacks to Create Thicker-Looking Hair," 5 Jan. 2019 These let Lovot recognize sounds, identify individual humans, and distinguish people and pets from furniture using thermal vision. James Vincent, The Verge, "Japan’s latest home robot isn’t useful — it’s designed to be loved," 20 Dec. 2018 Some DERs store energy, like batteries, fuel cells, or thermal storage like water heaters. David Roberts, Vox, "Clean energy technologies threaten to overwhelm the grid. Here’s how it can adapt.," 30 Nov. 2018 It is estimated that the eruption of Vesuvius released 100,000 times the thermal energy of the atomic bombs dropped on Hiroshima and Nagasaki in 1945, ejecting many tons of molten rock, pumice, and hot ash over the course of two days. Jennifer Ouellette, Ars Technica, "Extreme heat of Vesuvius eruption vaporized body fluids, exploded skulls," 9 Oct. 2018 The concept basically marries the idea behind thermal blowout brushes (like this) and self-curling irons like Beachwaver. Lindsay Schallon, Glamour, "Dyson Made a $500 Dryer That Literally Curls Your Hair for You," 9 Oct. 2018 Each gallon of water that evaporates and condenses carries about as much thermal energy into the atmosphere as that contained in 1 cup of gasoline. Douglas Fox, Popular Mechanics, "How Do Hurricanes Form? Disaster Science Explained," 10 Sep. 2018 Fortunately, the rover is equipped with eight heating units made out of plutonium that generate a tiny amount of thermal energy. Loren Grush, The Verge, "NASA’s Opportunity rover is in a deep sleep on Mars — but there’s hope it will wake up again," 13 June 2018 The clock will be driven by giant gears within a shaft in the mountain and powered by thermal energy harvested from the changes in temperature associated with the day/night cycle on the mountain above. NBC News, "A 10,000-year clock is being built under a mountain owned by Jeff Bezos," 26 Feb. 2018

Recent Examples on the Web: Noun

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 Officials are trying to start up several other thermal and hydroelectric plants to get at least some power back on the island. Fox News, "The Latest: 9 dead, 30 missing in northern Japan quake," 6 Sep. 2018 Apple has generally chosen not to go with the highest-end laptop GPUs in the MacBook Pro line, because those GPUs have necessarily come with big compromises in thermals and portability. Samuel Axon, Ars Technica, "2018 15-inch MacBook Pro review: Better, faster, stronger?," 24 July 2018 His daily wardrobe never veers far from a T-shirt over a long-sleeve thermal. Jessica Radloff, Glamour, "The Big Bang Theory," 25 Oct. 2018 Seko said utilities were planning to start up several other thermal and hydroelectric plants to provide at least some power. Fox News, "At least 7 dead, dozens feared buried after quake hits northern Japan," 2 Oct. 2018 The 13-, 15-, and 17-inch Inspiron 7000 two-in-ones now have the new thermal system found in the Inspiron Chromebook, featuring vents behind the hinges. Valentina Palladino, Ars Technica, "Dell tempts Pixelbook lovers with premium $599 Inspiron Chromebook 14," 29 Aug. 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.

See More

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

Keep scrolling for more

Learn More about thermal

Statistics for thermal

Last Updated

8 Jan 2019

Look-up Popularity

Time Traveler for thermal

The first known use of thermal was in 1742

See more words from the same year

Keep scrolling for more

More Definitions for thermal



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

thermals : thermal clothing or underwear


ther·​mal | \ ˈthər-məl \

Kids Definition of thermal

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


ther·​mal | \ ˈthər-məl \

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 \ adverb

Keep scrolling for more

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).


marked by shyness and lack of polish

Get Word of the Day daily email!

Test Your Vocabulary

Liar, Liar Quiz

  • alt-5761dbe2ba986
  • Someone who pretends to be sick in order to avoid work is a:
Name That Thing

Test your visual vocabulary with our 10-question challenge!

Syn City

Test Your Knowledge - and learn some interesting things along the way.


Love words? Need even more definitions?

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