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

The design eliminates flammable liquid electrolytes and thermal runaway risks, addressing long-standing safety concerns associated with conventional lithium-ion batteries. —Neetika Walter, Interesting Engineering, 6 Jan. 2026

In Brazil, the 2013 fire at Kiss nightclub caused by people setting off fireworks that ignited flammable soundproofing foam, killing more than 200 people, leading to fire safety reforms in that country as well. —The Editorial Board, Chicago Tribune, 4 Jan. 2026

Corrosion and rust may damage the tanks, allowing flammable propane to escape. —Lee Wallender, The Spruce, 4 Jan. 2026

The sparklers appear to have ignited what experts believe is acoustic paneling on the ceiling, a material designed to improve sound but that can also be highly flammable. —Kara Fox, CNN Money, 2 Jan. 2026

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