aux·​in ˈȯk-sən How to pronounce auxin (audio)
: any of various usually acidic organic substances that promote cell elongation in plant shoots and usually regulate other growth processes (such as root initiation): such as
: any of various synthetic substances (such as 2,4-D) resembling indoleacetic acid in activity and used especially in research and agriculture
auxinic adjective

Examples of auxin in a Sentence

Recent Examples on the Web During the experiments, the team found an increase in auxin, a plant growth hormone, in the roots. Elizabeth Gamillo, Discover Magazine, 13 July 2023 Plants control their root length and root direction, and development using hormones called auxins, and cytokinins, to name a few. Elizabeth Gamillo, Discover Magazine, 13 July 2023 By studying patterns of the plant hormone auxin, researchers have discovered that auxin concentrations cause asymmetry at the molecular and anatomical levels, altering gene expression and leaf shape. Discover Magazine, 2 May 2018 Rooting hormone contains plant hormones called auxins that help the plant root faster. Maryal Miller Carter, USA TODAY, 22 June 2023 Powdered Kelp Meal: Another all-natural powerhouse, this powder increases natural plant growth hormones such as auxins, cytokines, and gibberellins (aka: powerful plant hormones). Kristin Guy, Sunset Magazine, 28 Feb. 2023 Kelp’s main phytohormones are auxin, gibberellin and cytokinin. Jeff Lowenfels, Anchorage Daily News, 20 Apr. 2023 The growing tips of plants produce auxin — a hormone that tells cells to grow and divide — which is then sent to the rest of the plant. Christie Wilcox, Discover Magazine, 24 Aug. 2013 So, your stump will continue to synthesize auxin. oregonlive, 18 Mar. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'auxin.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


borrowed from German Auxin, from aux- (borrowed from Greek auxánein "to make grow, increase, strengthen," from aux- "grow" + -an-, verb formative marking completion) + -in -in entry 1 — more at wax entry 3

Note: The name Auxin was introduced by the German chemist Fritz Kögl (1897-1959) and his co-worker at the University of Utrecht, the Dutch chemist Arie Jan Haagen-Smit (1900-77), in the article "Über die Chemie des Wuchsstoffs (Communicated at the meeting of Dec. 19, 1931… by Prof. F.A.F.C. Went)," Koninklijke Akademie van Wetenschappen [Royal Netherlands Academy of Sciences], Proceedings of the Section of Sciences, vol. 34 (1931), pp. 1411-1416: "Wir schlagen für den Wuchsstoff die Bezeichnung Auxin (von auxánō [Greek letters] wachsen machen) vor, wobei es sich zur leichteren Namenbildung bei Derivaten empfehlen wird, hierunter die zugrundeliegende frei Säure zu verstehen" ("We suggest for the growth agent the designation auxin (from auxánō to cause to grow), to be recommended for the easier formation of derivative names, including the underlying free acid").

First Known Use

1933, in the meaning defined at sense 1

Time Traveler
The first known use of auxin was in 1933

Dictionary Entries Near auxin

Cite this Entry

“Auxin.” Dictionary, Merriam-Webster, Accessed 26 Feb. 2024.

Kids Definition


aux·​in ˈȯk-sən How to pronounce auxin (audio)
: a plant hormone that causes the shoot to grow in length and usually controls other growth processes (as root formation)

Medical Definition


aux·​in ˈȯk-sən How to pronounce auxin (audio)
: an organic substance that is able in low concentrations to promote elongation of plant shoots and usually to control other specific growth effects
broadly : plant hormone

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