flammable
adjective
Usage of Flammable, Inflammable, and Nonflammable
Flammable and inflammable look like opposites, but they both describe something that ignites easily and burns quickly. Inflammable arrived in English two centuries before flammable. Its prefix in- is not the one meaning "not," familiar from words like inactive and inaccurate. Instead it is another prefix altogether: in- as a form of -en-, meaning "to cause to be," as in the words indent and indebted. This fact is not obvious, however, and confusion about the meaning of inflammable persists. Using nonflammable is one way to ensure clarity when "not flammable" is the intended meaning.
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Why Inflammable Is Not the Opposite of Flammable
Combustible and incombustible are opposites but flammable and inflammable are synonyms. Why? The in- of incombustible is a common prefix meaning "not," but the in- of inflammable is a different prefix. Inflammable comes from Latin inflammare ("to inflame"), itself from in- (here meaning "in" or "into") plus flammare ("to flame"). Flammable also comes from flammare. In the early 20th century, firefighters worried that people might think inflammable meant "not able to catch fire," so they adopted flammable and nonflammable as official safety labels and encouraged their use to prevent confusion. In general use, flammable is now the preferred term for describing things that can catch fire, but inflammable is still occasionally used with that meaning as well.
Examples of flammable in a Sentence
Brandee Gruener, Southern Living, 27 Jan. 2026
Gas ovens pose a dangerous carbon monoxide risk that can lead to poisoning or death, while electric ovens can be a fire hazard, melting knobs or igniting nearby flammable items.
—Jonathan Limehouse, USA Today, 24 Jan. 2026
Soundproofing foam, soft and highly flammable, had been stretched across a low basement ceiling.
—Elena Clavarino, Air Mail, 24 Jan. 2026
Be cognizant of overloading extension cords and be careful to keep heaters and flammable items away from other heat-generating devices.
—Lauren Caruba, Dallas Morning News, 23 Jan. 2026
See All Example Sentences for flammable
Cite this Entry
“Flammable.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/flammable. Accessed 4 Feb. 2026.
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flammable
adjective
