reagent

Etymology

It is formed from English re- + agent,^[2][3][4][5] by analogy: the noun stands in the same relation to react as agent does to act.^[2][5][6] Barnhart takes agent here in its chemical sense, a substance that produces a reaction (1756), and thinks the word was perhaps vaguely influenced by French réagir (“to react”).^[4] The OED compares New Latin reagens, recorded from 1703 or earlier,^[2] and Merriam-Webster Unabridged derives the word from it, the present participle of reagō (“to react”).^[7]

Earliest recorded meaning

A person or thing that is acted upon or reacts to something; a reactive substance or force: 1656, in the English translation of Hobbes's Elements of Philosophy.^[2]

Semantic evolution

The chemical sense appears in 1784, in E. Cullen's translation of Bergman's Physical and Chemical Essays:^[2][7] at first a substance used to test for the presence of another substance by the reaction it produced, and later any substance used in chemical reactions.^[5][2] Etymonline dates the chemical sense to 1785 and Barnhart to 1797.^[3][4] Reagents named after chemists followed, such as the Grignard reagent and Schiff's reagent,^[5] and Emerson used the word figuratively: "Civilization is a reagent, and eats away the old traits".^[5] Merriam-Webster Unabridged also records it for the subject of a psychological experiment.^[7]

Timeline

• 1656 – a thing that is acted upon or reacts; a reactive force.^[2]
• 1784 – in chemistry, a substance used to test for other substances.^[2][7] Etymonline dates it to 1785 and Barnhart to 1797.^[3][4]

Meanings

Noun

1. A substance used in a chemical reaction, especially to detect, measure or prepare other substances: The lab ran out of the reagent needed for the assay.^[8][7][2][5]
2. The subject of a psychological experiment.^[7]
3. A person or thing that is acted upon by something or reacts to it.^[2]

Word family

• Grignard reagent

Related words

• react
• agent
• act

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
5. ^ a b c d e f Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
6. ^ Partridge, Eric (1966), Origins: A Short Etymological Dictionary of Modern English, 4th ed., London: Routledge & Kegan Paul
7. ^ a b c d e f Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
8. ^ Collins English Dictionary (2023), Glasgow: HarperCollins