thermal

American  

[thur-muhl] / ˈθɜr məl /

adjective

1. Also of, relating to, or caused by heat or temperature.

   Buildings and sealed surfaces have a higher thermal capacity than soil and give up their heat more slowly at night.

   We speed up composting using a thermal treatment.

2. of or relating to hot springs or hot baths.

   The bubbly, hot spring pool derives its name from the character of its thermal waters.

3. designed to aid in or promote the retention of body heat.

   We keep a thermal blanket in the car during winter, just in case.

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noun

• thermals
  plural

1. Meteorology. a rising air current caused by heating from the underlying surface, especially such a current when not producing a cloud.

2. thermal energy.

3. thermals. thermal underwear.

thermal British  

/ ˈθɜːməl /

adjective

1. Also: thermic.  of, relating to, caused by, or generating heat or increased temperature

2. hot or warm

   thermal baths

   thermal spring

3. (of garments or fabrics) specially designed so as to have exceptional heat-retaining properties

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noun

1. meteorol a column of rising air caused by local unequal heating of the land surface, and used by gliders and birds to gain height

2. (plural) thermal garments, esp underclothes

thermal Scientific  

/ thûr′məl /

1. Relating to heat.

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1. A usually columnar mass of warm air that rises in the lower atmosphere because it is less dense than the air around it. Thermals form because the ground surface is heated unevenly by the Sun. The air usually rises until it is in equilibrium with the air surrounding it.

Usage

What does thermal mean? Thermal means caused by or related to heat or temperature. The word thermal is used in science to describe a specific kind of energy: thermal energy. Thermal energy is produced by heating up molecules and atoms until they move fast enough to collide into each other. What we experience as heat is a flow of thermal energy. Geothermal energy involves heat generated by the earth. Outside of science, the word thermal is most often used to mean that something is related to high temperatures or something intended to retain body heat, as in Thermal gloves are insulated to keep your hands warm in the winter. Thermal is sometimes used in reference to thermal springs, also known as hot springs. The plural noun thermals is sometimes used as shorthand for thermal underwear, which is designed to retain body heat. The word thermic can be used as a synonym of thermal, typically in technical ways in fields such as science or engineering. Example: Thermal maps show areas of higher and lower temperatures.

Other Word Forms

Derived Forms

• hyperthermal
  adjective
• nonthermal
  adjective
• hyperthermally
  adverb
• nonthermally
  adverb
• thermally
  adverb

Inflected Forms

Nouns

• thermals
  plural

Etymology

Origin of thermal

First recorded in 1750–60; therm- + -al ¹

Explanation

If it has to do with heat, it’s thermal. Wearing a thermal shirt under your sweater helps you stay warm on a brutally cold day. Your thermal coffee mug keeps your coffee hot. The Greek word therme, meaning “heat,” is the origin of the adjective thermal. Something that is thermal is hot, retains heat, or has a warming effect. If your sweatshirt has a thermal lining, its texture might remind you of a waffle-that's what traps your body heat. Also, there are large currents of warm air that flow upwards — these are what gliders or big birds like hawks ride to stay afloat — one type of those currents is called a “thermal.”

Example Sentences

See Examples For:

thermal thermals

Larger drones that have militarily sensitive capabilities, like thermal imaging, as well as “critical” drone components will be subject to a 100% tariff.

From MarketWatch ● Aug. 14, 2026

Bigger drones that have militarily-sensitive abilities such as thermal imaging are subject to a 100% ad valorem tariff, along with certain critical components.

From The Wall Street Journal ● Aug. 14, 2026

Through the Unruh effect, an accelerating observer would perceive empty space as a thermal environment.

From Science Daily ● Aug. 3, 2026

The seven thermal power plants that form the national grid's backbone have all been in operation for more than 40 years, and are in various states of disrepair.

From Barron's ● Aug. 2, 2026

Eagles, for example, identify thermal columns rising from the ground, spread their giant wings and allow the hot air to lift them upwards.

From "Sapiens: A Brief History of Humankind" by Yuval Noah Harari

"I just hope that the Kates and Cathys have got their thermals and their rain ponchos because they might need them."

From BBC ● Jul. 26, 2026

In the first, a quadrotor drone was able to observe four hovering white balls while avoiding four orange balls, all while navigating an airfield rife with randomly occurring, dangerous air currents, or thermals.

From Science Daily ● Dec. 4, 2024

As spectators chant and funnel into the tree-lined stadium, the day starts to warm, which is when spotted lanternflies can be found rising into the air on thermals.

From National Geographic ● Aug. 31, 2023

Vultures, another raptor, are easy to spot in the early afternoon because they “get up on the thermals and fly miles and miles and miles” looking for food, he said.

From New York Times ● Jun. 29, 2023

Ahead of them, high in the sky, circling on the hot air currents, were the night-gaunts, dozens of them, riding the thermals.

From "The Graveyard Book" by Neil Gaiman