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reactant

American  
[ree-ak-tuhnt] / riˈæk tənt /

noun

  1. a person or thing that reacts.

  2. Also called interactant.  Chemistry. any substance that undergoes a chemical change in a given reaction.

reactant British  
/ rɪˈæktənt /

noun

  1. a substance that participates in a chemical reaction, esp a substance that is present at the start of the reaction Compare product

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
reactant Scientific  
/ rē-ăk′tənt /

  1. A substance participating in a chemical reaction, especially one present at the start of the reaction.

Etymology

Origin of reactant

First recorded in 1925–30; react + -ant

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

"We were able to vary the behavior and effective size of the ultrasmall pores by changing the composition and pH of the reactant solutions," reports Tomoji Kawai, senior author.

From Science Daily • Feb. 19, 2026

This process involves destabilizing one of the aromatic rings in quinoline, using light and sometimes a catalyst, so that a reactant can 'latch' onto the ring, forming the target compound.

From Science Daily • Jun. 19, 2024

Once the temperature is sufficiently low, the concentration of the reactant gases on the catalyst surface increases and the reaction picks up speed again.

From Science Daily • Oct. 5, 2023

If temperature or reactant concentration is increased, the rate of a given reaction generally increases as well.

From Textbooks • Feb. 14, 2019

They cool the reactant fuel to keep it from getting too hot and wildcatting.

From Treachery in Outer Space by Glanzman, Louis

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.