What does flammable mean?
Flammable is an adjective describing materials that catch fire easily and burn readily — petrol, acetone, paper, dry brush, and many gases all qualify. It is the standard term in safety signage, shipping regulations, and everyday speech, prized for being unambiguous. That clarity is deliberate: English long relied on the older word 'inflammable', which means precisely the same thing, yet its in- prefix led many readers to assume it meant 'not flammable' — a potentially lethal misunderstanding. In response, mid-twentieth-century safety authorities, particularly in the United States, promoted 'flammable' as the safer choice, and it has since become the dominant form on warning labels worldwide. The word carries no emotional charge itself, but its presence almost always signals danger or caution nearby. Derived forms include the noun 'flammability' and the adjective 'nonflammable'. For anyone handling fuels, chemicals, or fire, knowing this word — and what it does not mean — is genuinely useful.
adjectiveCapable of catching fire and burning easily.
- (of a substance) easily ignited and capable of burning rapidly
"The factory stores its solvents in specially marked flammable cabinets."
"Keep flammable materials away from open flames."
"The vapour from the solvent is highly flammable, even at room temperature."
'Flammable' and 'inflammable' mean exactly the same thing — a trap so dangerous that safety experts pushed 'flammable' onto warning labels to stop people from dousing fires near 'inflammable' liquids.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of flammable
Flammable derives from the Latin verb flammare, meaning 'to set on fire', itself rooted in flamma, 'flame'. It entered English in the early nineteenth century as a back-formation from the older adjective inflammable, which had been borrowed via French and Latin with the prefix in- meaning 'into, upon' (intensifying, not negating). As confusion over that prefix grew, flammable was deliberately revived as a clearer alternative. Its Latin relatives include conflagration and flagrant, both tracing back to the same root of burning.
Related word forms
How flammable is actually used
Preferred over 'inflammable' on warning labels and in safety contexts because the negative-sounding prefix of 'inflammable' is frequently misunderstood as meaning 'not flammable'. Common in technical, regulatory, and everyday use; neutral in connotation but strongly associated with hazard warnings.
Easily confused with flammable
Inflammable means the same thing as flammable — both mean easily set on fire — but the in- prefix misleads people into thinking it means 'not flammable', which is why safety labels now prefer flammable.