Thermal

How to spell thermal

7 letters · 2 syllables

How to pronounce thermal

Say the part in capitals loudest.

What does thermal mean?

1. adjectiveRelating to heat or temperature, or designed to retain warmth.
2. nounA rising current of warm air that gliders and soaring birds use to gain height.

Thermal in a sentence

• adjective

  The campers packed thermal underwear for the cold nights.

• noun

  The glider pilot circled inside a thermal to climb higher.

• adjective

  The new windows have a thermal coating that keeps the heat indoors.

• noun

  Hawks ride a thermal for hours without flapping their wings.

Where does thermal come from?

Language of origin: Greek

The word traces back to the Greek thermē, meaning 'heat', and the related adjective thermos, meaning 'hot' or 'warm'. French naturalists of the eighteenth century coined thermal to describe hot mineral springs, and English borrowed that French form around the 1750s. From the literal sense of warm waters, the meaning broadened to cover anything connected with heat or temperature, which is how we arrived at thermal insulation, thermal imaging, and thermal underwear. The same Greek root powers a whole family of familiar words: a thermometer measures heat, a thermos flask keeps drinks hot, and a thermostat regulates temperature. Keeping that therm- core in mind explains the spelling: the tricky part is simply the unstressed -al ending, pronounced as a faint 'uhl'.

How the word is built

• therm- (from Greek thermē: heat)
• -al (adjective/noun suffix)