Vocabulary
B2
6 min read
Updated 15 June 2026
Quick Answer
Despite appearances, flammable and inflammable are synonyms: both mean “easily set on fire.” The in- in inflammable is not a negative prefix — it comes from the Latin verb inflammare (to set alight), not from “not.” Because inflammable is dangerously easy to misread as “not flammable,” modern safety labels prefer flammable. The genuine opposite is non-flammable.
Flammable and inflammable are one of English’s most dangerous confusions, because the difference learners expect does not exist. People assume the in- prefix reverses the meaning, the way it does in invisible or incorrect. It does not. Both words mean a material burns easily. The only safe opposite is non-flammable. Understanding why this happens — and which word to use on a warning — can genuinely matter for safety.
At a Glance: Flammable vs Inflammable
| Word | Part of Speech | Pronunciation | Core Meaning |
|---|
| flammable |
adjective |
/ˈflæməb(ə)l/ |
easily set on fire; catching fire quickly |
| inflammable |
adjective |
/ɪnˈflæməb(ə)l/ |
easily set on fire (same meaning as flammable) |
Using “Flammable”
Flammable means a substance catches fire easily and burns quickly. It is the clearer, preferred word on safety labels and warnings precisely because it cannot be misread. Petrol, alcohol, and many solvents are flammable.
When to use it
- Safety labels and warnings (preferred form): highly flammable
- Describing materials that burn easily: flammable liquids, flammable gas
- Everyday and technical writing alike
- The clearer choice when safety is involved
- Related word: flammability
Keep the flammable liquids away from the cooker.
The label warns that the spray is highly flammable.
Petrol is extremely flammable, so never smoke nearby.
These flammable materials must be stored in a metal cabinet.
Dry leaves are very flammable in summer.
Using “Inflammable”
Inflammable is the older word and means exactly the same as flammable: easily set on fire. The in- here is an intensifying prefix from Latin, not a negative one. Because so many people misread it as “not flammable,” safety authorities began promoting flammable in the twentieth century. Inflammable still appears in older texts and formal or literary writing.
When to use it
- Older or literary texts: inflammable vapours
- Formal British and historical writing
- Figurative use — quick to anger: an inflammable temper
- Note: it is a synonym of flammable, never its opposite
- Related words: inflame, inflammation, inflammatory
The Victorian warehouse was packed with inflammable goods.
Old film stock was notoriously inflammable.
He has an inflammable temper and flares up at the smallest thing.
The cargo manifest listed several inflammable substances.
Her speech was full of inflammable language designed to provoke.
The Key Difference
There is no difference in meaning — that is the whole point. Flammable and inflammable both mean “burns easily.” The only real distinction is clarity and register: flammable is the modern, unambiguous choice used on warnings, while inflammable is older and risks being misread. For the genuine opposite — something that does not catch fire — you must use non-flammable (or fire-resistant).
Memory Tip
Don’t be fooled by the in-. The in- in inflammable comes from inflame (to set on fire), so it adds to the fire rather than cancelling it. If you ever feel unsure on a real label, picture the safe opposite: only non-flammable means “will not burn.” When in doubt about safety, treat both flammable and inflammable as dangerous.
Common Mistakes
This jacket is inflammable, so it won't catch fire.
This jacket is non-flammable, so it won't catch fire. (inflammable means it DOES burn; use non-flammable for the opposite)
The two cans are different: one flammable, one inflammable.
Both cans are the same: flammable and inflammable mean the same thing. (they are synonyms, not opposites)
Choose inflammable curtains for fire safety.
Choose non-flammable (or fire-resistant) curtains for fire safety. (for safety you want non-flammable)
The gas is non-inflammable and totally safe.
The gas is non-flammable and totally safe. (the standard safe-label term is non-flammable)
Frequently Asked Questions
Do flammable and inflammable mean the same thing?
Yes, surprisingly they do. Both flammable and inflammable mean easily set on fire. They are synonyms, not opposites. The confusion arises because the in- prefix usually means not, as in invisible or incorrect. But in inflammable, the in- comes from the Latin inflammare, meaning to set alight, so it actually reinforces the idea of burning. Both words describe a material that catches fire easily, so you should treat them identically when thinking about safety.
What is the opposite of flammable?
The opposite of flammable is non-flammable, meaning a material that does not catch fire easily. You may also see fire-resistant, fireproof, or non-combustible for things that resist burning. The crucial point is that the opposite is not inflammable, because inflammable means the same as flammable. If you want to say something will not burn, always use non-flammable or a similar term, never inflammable, which would dangerously imply the opposite of what you mean.
Why does inflammable not mean 'not flammable'?
Because the in- in inflammable is not the negative prefix. It comes from the Latin verb inflammare, meaning to set on fire or to inflame, the same root behind inflame and inflammation. So inflammable literally means able to be set alight. This is different from words like inactive or invisible, where in- does mean not. The mismatch between expectation and reality is exactly why inflammable is considered confusing and why flammable is now preferred on labels.
Which word should I use on a safety label?
Use flammable. Safety authorities and standards bodies moved towards flammable during the twentieth century precisely because inflammable is so easily misread as not flammable, which could lead to dangerous mistakes. On modern warnings you will typically see highly flammable rather than inflammable. If you need to label something that will not burn, write non-flammable. The goal of a safety label is instant clarity, and flammable and non-flammable give the clearest possible contrast.
Is inflammable an old-fashioned word?
Inflammable is the older of the two words and is now less common in everyday and safety contexts, but it has not disappeared. You will still meet it in older texts, formal or literary writing, and figurative uses such as an inflammable temper. It is not wrong, just potentially confusing. Because flammable is clearer and now standard on warnings, most modern writers prefer it, reserving inflammable for stylistic effect or when quoting historical material.
Can inflammable be used figuratively?
Yes. Inflammable is often used figuratively to describe people or situations that are easily provoked or quick to flare up, such as an inflammable temper or an inflammable political situation. This figurative sense connects to the related words inflame and inflammatory, as in inflammatory remarks that stir up strong feeling. Flammable is rarely used this way; it stays closer to literal fire. So for emotional or metaphorical heat, inflammable and inflammatory are the more natural choices.
What does non-flammable mean?
Non-flammable means a material does not catch fire easily and will not readily burn. It is the true opposite of both flammable and inflammable. You will see it on safety labels for products designed to resist fire, such as non-flammable cleaning sprays or building materials. If a label says non-flammable, the manufacturer is claiming the item is safe from easy ignition. Always read carefully, because the presence or absence of the prefix non- completely reverses the meaning.
Are flammable and combustible the same?
They are related but not identical in technical safety contexts. Broadly, both flammable and combustible materials can burn. In many safety classifications, however, flammable refers to substances that ignite very easily at lower temperatures, while combustible refers to substances that can burn but need more heat to ignite. In everyday English the two often overlap. For precise safety work, check the relevant standard, but for general purposes both describe materials that catch fire, unlike non-flammable items.
How do you pronounce inflammable?
Inflammable is pronounced /ɪnˈflæməbəl/, roughly in-FLAM-uh-bul, with the stress on the second syllable, flam. Flammable is pronounced /ˈflæməbəl/, FLAM-uh-bul, with the stress on the first syllable. Both contain the clear flam sound linked to flame. Saying them aloud can help you remember that they share the same flame root and therefore the same meaning, rather than being opposites as the spelling of inflammable might suggest.
Is inflammable correct in modern English?
Yes, inflammable is still a correct English word with the same meaning as flammable. It is not an error. However, because it is so easily misunderstood as not flammable, careful writers and safety bodies prefer flammable in any context where clarity matters, especially warnings. You can still use inflammable in formal, literary, or figurative writing, but if there is any chance of confusion, particularly around fire safety, choose flammable instead to avoid a potentially dangerous misreading.
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