thermal

Pronunciation

• IPA: /ˈθɜːməl/ (UK); /ˈθɝməl/ (US)^[1]

Etymology

It is borrowed from French thermal, a word of Buffon's,^[2][3][4] formed from Greek θέρμη (thérmē, “heat, feverish heat”) with the suffix -al,^[2][3][5] from PIE Proto-Indo-European *gwher- (“to heat, warm”) (see warm).^[3][2]

Earliest recorded meaning

Of or having to do with hot springs: 1756 in Barnhart, Etymonline and the OED;^[2][3][6] Merriam-Webster dates the word to 1742.^[5]

Semantic evolution

The sense relating to heat, measured or caused by heat, is recorded by 1837.^[2][3][6] A figurative sense, passionate, is from 1866.^[6] The noun, a rising current of warm air used by gliders and birds, is from 1933,^[3][6] and thermalling, soaring in thermals, from 1936.^[6] A thermal neutron is from 1936,^[6] and clothing designed to keep in heat, especially underwear, from 1970.^[6]

Timeline

• 1756 – of hot springs.^[6]
• 1837 – relating to heat.^[6]
• 1866 – passionate.^[6]
• 1933 – a rising current of air (noun).^[6]
• 1970 – heat-retaining clothes.^[6]

Modern meaning

Adjective

1. Of, relating to, caused by or producing heat.
2. Designed to retain body heat: thermal underwear.
3. Of springs or baths, naturally hot.

Noun

1. A rising current of warm air, used by gliders and birds to gain height.
2. (thermals) Thermal underclothes.

Word family

• thermally

Related words

• therm
• thermo-
• thermometer
• thermostat
• thermos
• hypothermia
• warm

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
3. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
5. ^ a b Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
6. ^ a b c d e f g h i j k l Simpson, J. A.; Weiner, E. S. C., eds. (1989), The Oxford English Dictionary, 2nd ed., Oxford: Clarendon Press