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
Alexandra Banner, CNN Money, 1 Dec. 2025
Earlier, police arrested two directors and an engineering consultant of Prestige Construction, a firm identified by the government as doing maintenance on Wang Fuk Court for more than a year, on suspicion of manslaughter for using unsafe materials, including flammable foam boards blocking windows.
—Jessie Pang, USA Today, 29 Nov. 2025
Keep them away from flammable items, such as dry pine needles and synthetic materials, and let the bulbs cool completely before handling.
—Kylie Petty, Better Homes & Gardens, 29 Nov. 2025
Vincent Ho, founder of Hong Kong think tank the Institute of Building Safety, listed the flammable bamboo scaffolding, the close proximity of the buildings and the possible presence of materials that were not sufficiently fire resistant among plausible reasons.
—Shawna Kwan, Fortune, 28 Nov. 2025
See All Example Sentences for flammable
Cite this Entry
“Flammable.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/flammable. Accessed 8 Dec. 2025.
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flammable
adjective
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