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
ABC News, 11 June 2026
Investigators allege renovation bosses used flammable scaffolding netting and foam boards, obstructed escape routes and falsified oversight records, putting profit over safety in the Wang Fuk Court housing complex.
—Kanis Leung, Los Angeles Times, 10 June 2026
Helios Horizon performs first flight with solid-state batteries Solid-state batteries replace the flammable liquid electrolyte found in conventional lithium-ion cells with a solid material.
—Chris Young, Interesting Engineering, 10 June 2026
The issue could heat flammable materials and potentially cause a fire, even when the vehicle is turned off.
—Sacbee.com, 10 June 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 17 Jun. 2026.
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flammable
adjective
