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 plan contends the deer are eating the native grasses, which harm the island’s ecosystem and increase the growth of more flammable, invasive grasses that can fuel a wildfire. —Steve Scauzillo, Daily News, 9 Mar. 2026

The grout between tiles is a crucial barrier to heat from the tile backer, which is often flammable. —Kamron Sanders, Better Homes & Gardens, 8 Mar. 2026

Always check your oven’s manual or control panel to confirm the drawer’s function and avoid storing flammable items inside. —Caroline Lubinsky, Martha Stewart, 7 Mar. 2026

The massive building is filled with thousands of items, including hazardous and flammable materials. —David Goodhue, Miami Herald, 7 Mar. 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