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

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

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

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

For decades, this thermal barrier has been one of the toughest challenges in engineering.

From Science Daily • Apr. 7, 2026

Sensors on Orion recorded how its power and thermal systems coped for nearly an hour without direct sunlight and with rapid swings in heating and cooling as it moved through the eclipse.

From BBC • Apr. 6, 2026

Fire Administration, potentially leading to a process known as thermal runaway, in which the battery ignites through a self-sustaining chemical reaction that is impossible to stop until it runs out on its own.

From Los Angeles Times • Apr. 6, 2026

Peabody maintained 2026 full-year shipment targets, but analysts see them at risk, despite high thermal coal prices.

From Barron's • Mar. 30, 2026

Waterproof boots, a snowsuit that covers me from head to toe, thermal gloves.

From "Catching Fire" by Suzanne Collins