thermostat

Etymology

It is formed from English thermo- + -stat,^{[2][3][4][5][6]} or, as the OED puts it, from thermo- and Ancient Greek στατός (statós, “standing”), like heliostat.^[7][8] Klein compares aerostat and static.^[8] The combining form thermo- is from θερμός (thermós, “hot, warm”), from Proto-Indo-European *gʷʰer- (“to heat, warm”).^[2] The element -stat, used from the 18th century for devices that stabilise or regulate something, is first recorded in heliostat (1742),^[2] and comes through French -stat (as in héliostat and aérostat) and post-classical New Latin -stata from Ancient Greek -στάτης (-státēs), built on the root of ἱστάναι (histánai, “to cause to stand, set”).^[7]

Earliest recorded meaning

An automatic apparatus for regulating temperature: 1831 in Etymonline, Barnhart, Merriam-Webster and the 1989 edition of the OED;^{[2][3][9][10]} the revised OED's first quotation is from Andrew Ure's Philosophy of Manufactures (1835).^[7]

Semantic evolution

The OED describes the early thermostats as devices in which the expansion of metals or of a gas acts directly on the source of heat or the ventilation.^[7] From 1881 the word also named an apparatus that warns of a rise in temperature, an automatic fire alarm,^[7][4] a sense the Shorter Oxford calls now rare.^[4] The verb, to regulate the temperature of something with a thermostat, is dated 1924 by Merriam-Webster^[5][9] and 1940 in the revised OED,^[7] while the 1989 edition of the OED dated it to 1839.^[10] The adjective thermostatic is recorded from the mid 19th century.^[4]

Timeline

• 1831 – an automatic device for regulating temperature.^[2][3][10] The revised OED's first record is from 1835.^[7]
• 1881 – a device giving warning of a rise in temperature; an automatic fire alarm.^[7]
• 1924 – verb, to provide with or control by a thermostat.^[5][9] The revised OED dates the verb to 1940.^[7]

Meanings

Noun

1. A device that automatically keeps a system at a set temperature by switching a heating or cooling apparatus on and off, often by means of a bimetallic strip: She turned down the thermostat before leaving for the weekend.^[11][5][12]
2. A similar device that sets off equipment such as a sprinkler or a fire alarm when a certain temperature is reached.^[11][5][7]
3. In computer simulation, an algorithm that keeps a simulated system at a set temperature by adding or removing heat.^[1]

Verb

1. To fit with a thermostat, or to regulate the temperature of something by one.^[5][7][4]

Word family

• thermostatic
• thermostatically

Related words

• heliostat
• aerostat
• static
• thermal

References

1. ^ a b Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
3. ^ a b c Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
4. ^ a b c d e Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
5. ^ a b c d e f Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
6. ^ Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
7. ^ a b c d e f g h i j k Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
8. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
9. ^ a b c Merriam-Webster's Collegiate Dictionary (2003), 11th ed., Springfield, Mass.: Merriam-Webster
10. ^ a b c Simpson, J. A.; Weiner, E. S. C., eds. (1989), The Oxford English Dictionary, 2nd ed., Oxford: Clarendon Press
11. ^ a b Collins English Dictionary (2023), Glasgow: HarperCollins
12. ^ The American Heritage Dictionary of the English Language (1992), 3rd ed., Boston: Houghton Mifflin