Flammable and inflammable both mean “capable of burning easily” — they are not opposites. The true opposite of both is non-flammable.
The Core Difference
“Flammable” is the modern, widely-used adjective meaning able to catch fire and burn easily: flammable liquids, flammable gas. It is preferred on warning labels because it is unambiguous.
“Inflammable” means the same thing — capable of burning — even though the prefix “in-” usually means “not”. Here it comes from Latin “inflammare” (to set alight), not a negative prefix. Because it looks negative, it is now avoided on safety signs.
- capable of burning, preferred on labels → flammable: flammable materials
- same meaning, older/riskier word → inflammable: inflammable gas cylinders
Flammable and Inflammable in Context
This warehouse stores flammable chemicals.
The sign warned that the fabric was inflammable and burned quickly.
Petrol is a highly flammable liquid.
Old cotton curtains can be surprisingly inflammable.
Always keep flammable items away from open flames.
Common Mistakes
| Incorrect | Correct | Why |
|---|---|---|
| ✗ inflammable means it cannot burn | ✓ inflammable means it CAN burn | same meaning as flammable |
| ✗ this material is not inflammable, so it is safe near fire | ✓ this material is non-flammable, so it is safe near fire | clear negative form |
| ✗ flammable and inflammable are opposites | ✓ flammable and inflammable are synonyms | identical meaning |
| ✗ the label said inflammable, so I relaxed | ✓ the label said inflammable, so I stayed cautious | still means it burns |
| ✗ a non-inflammable jacket | ✓ a non-flammable jacket | modern negative form |
Both FLAMMABLE and INFLAMMABLE mean “can catch FLAME”. The “in-” in inflammable is NOT a negative — it comes from Latin “inflame”. If you need the true opposite, add “non-”: non-flammable.
Related Questions
- Flammable vs Inflammable — full confusing-words comparison page with additional examples and exercises.
- All Confusing Words — browse all 300+ word-pair guides.
- All Questions — more quick-answer pages.
- Grammar Quiz — test your knowledge of confusing word pairs.
Frequently Asked Questions
Why does "inflammable" not mean "cannot burn"?
Because its “in-” prefix comes from the Latin verb “inflammare”, meaning “to set on fire”, not from the negative Latin prefix “in-” (as in “invisible”). Historically, “inflammable” came first and simply meant “capable of being inflamed”.
Why do safety labels now prefer "flammable"?
Because so many people mistakenly read “inflammable” as meaning “not flammable”, safety organisations switched to the unambiguous “flammable” on warning labels to prevent dangerous misunderstandings.
What is the correct word for something that cannot burn?
“Non-flammable” (or less commonly “incombustible”) is the correct, unambiguous term for materials that do not catch fire easily.
Is "inflammable" still used today?
Yes, especially in British English and in older or international contexts, but it is increasingly avoided in favour of “flammable” specifically because of the risk of misreading it as a negative.
Are flammable and combustible the same thing?
They are closely related but technically different in fire science: “flammable” materials ignite easily at normal temperatures, while “combustible” materials can burn but may require higher temperatures to ignite.
What does "inflammation" have to do with "inflammable"?
Both come from the same Latin root “inflammare” (to set alight/to inflame), which explains why medical “inflammation” (redness, heat, swelling) shares its origin with words about fire, even though the meanings later diverged.
Which word should I use in a safety report?
Use “flammable” for clarity, and “non-flammable” for the opposite. Avoid “inflammable” in safety documentation because of the risk of it being misread.
Is this pair a true synonym pair or a confusing pair?
It is unusual: unlike most “confusing words” pairs, flammable and inflammable are not different in meaning at all — the confusion comes from the misleading appearance of the prefix, not from an actual difference in definition.
Are there other words with this same misleading "in-" pattern?
Yes, though rare — “invaluable” is a similar case: it does not mean “without value”, but rather “so valuable that its worth cannot be calculated”.
What should I remember most about this pair?
That they are synonyms, not opposites, and that the safe, modern choice for warning labels and formal writing is “flammable”, with “non-flammable” as its true opposite.