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retardant

[ri-tahr-dnt]
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noun Chemistry.
  1. any substance capable of reducing the speed of a given reaction.
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adjective
  1. retarding or tending to retard (usually used in combination): fire-retardant construction materials.
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Origin of retardant

First recorded in 1635–45; retard + -ant
Related formsre·tard·ance, re·tard·an·cy, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for retardance

retardant

noun
  1. a substance that reduces the rate of a chemical reaction
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adjective
  1. having a slowing effect
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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

Word Origin and History for retardance

n.

1550s, "retardation," from Middle French retardance, from retarder (see retard (v.)). In reference to resistance to fire, 1948.

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retardant

adj.

1640s, from retard (v.) + -ant or from Latin retardantem (nominative retardans), present participle of retardare. From 1952 as a noun, "retardant substance."

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Online Etymology Dictionary, © 2010 Douglas Harper