flammable

adjective

flam·​ma·​ble ˈfla-mə-bəl 

: capable of being easily ignited and of burning quickly

flammable noun

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.

Synonyms of flammable

• combustible
• explosive
• inflammable

Examples of flammable in a Sentence

avoid wearing loose flammable clothing when using the blowtorch

Recent Examples on the Web

Residents and visitors are urged to properly dispose of cigarette butts, matches, and any other flammable items in appropriate containers. —Nc Weather Bot, Charlotte Observer, 16 Nov. 2025

That’s because well-off Angelenos tend to live on mountains and hillsides and in canyons that are covered in highly flammable chaparral, which are an excellent breeding ground for rapidly spreading fires, driven by Santa Ana winds of up to 100 mph. —Todd Longwell, Variety, 12 Nov. 2025

But future designs may allow for the 3D printer to create a concrete roof, removing anything flammable from the home’s exterior. —Jake Goodrick, Sacbee.com, 8 Nov. 2025

Make sure the tank is not near other flammable materials, like gas cans or paint, when storing it for winter. —Brandee Gruener, Southern Living, 7 Nov. 2025

Word History

Etymology

Latin flammare to flame, set on fire, from flamma

First Known Use

1813, in the meaning defined above

Rhymes for flammable

• inflammable
• nonflammable
• programmable

Kids Definition

flammable

adjective

flam·​ma·​ble ˈflam-ə-bəl 

: capable of being easily set on fire and of burning rapidly

a flammable liquid

flammability

ˌflam-ə-ˈbil-ət-ē

noun

flammable noun