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.

Did you know?

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

Researchers blame a number of factors, including climate change causing fuel to dry out and be more flammable, a record drought, tens of millions of tons of dead trees from Hurricane Helene, and the vast area where dense forests and high numbers of people try to coexist. —Seth Borenstein, Los Angeles Times, 26 Apr. 2026

Over the last 50 years, industrial tree plantations have sprung up in the region, growing mainly non-native pines and eucalyptus, which are especially flammable. —Stefano Pozzebon, CNN Money, 26 Apr. 2026

People in this area are urged to properly dispose of cigarette butts, matches, and any other flammable items in appropriate containers. —Nc Weather Bot, Charlotte Observer, 25 Apr. 2026

That includes clearing dead or dying vegetation within 100 feet of all structures, landscaping with fire-resistant plans and non-flammable ground cover, and disposing of landscaping debris in other ways. —City News Service, San Diego Union-Tribune, 25 Apr. 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