retardant

American  

[ri-tahr-dnt] / rɪˈtɑr dnt /

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.

retardant British  

/ rɪˈtɑːdənt /

noun

1. a substance that reduces the rate of a chemical reaction

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adjective

1. having a slowing effect

Other Word Forms

• retardance noun
• retardancy noun

Etymology

Origin of retardant

First recorded in 1635–45; retard + -ant

Explanation

A retardant is anything that prevents something from happening, or inhibits it from growing or spreading. Using a rust retardant on your car, for example, should help keep it from getting rusty. A fire or flame retardant is a type of chemical that stops fire from starting or spreading. Sometimes fire retardants are sprayed or dumped on a fire to put it out, like the foam fire retardant you might spray from a hand-held fire extinguisher onto a grease fire in a kitchen. Retardant comes from the verb retard, "make slow, or make slower."

Example Sentences

Among the synthetic products, 19 claimed to be flame retardant, three were labeled water resistant, nine advertised heat resistance, and three promoted "green" claims such as "no PVC" or "non-toxic."

From Science Daily • Feb. 19, 2026

Gardner previously said that more than 100 firefighters used hoses to put a “wet line” around the Balcom fire perimeter, while bulldozers cut away vegetation in its path and aircraft caked the ground with retardant.

From Los Angeles Times • Jan. 30, 2026

Firefighters responded with a C-130 air tanker, dropped retardant and created containment lines around the fire.

From Los Angeles Times • Jan. 30, 2026

He says if the foam had been fire retardant it would have smouldered, not burned.

From BBC • Jan. 17, 2026

The colorful fire retardant drew Akira’s eye to the front line of the fire, and she saw a group of tiny figures using axes and bulldozers to fight the blaze in the valley.

From "Two Degrees" by Alan Gratz