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"Flammable" and "inflammable" mean exactly the same thing: capable of catching fire easily.
Side-by-side comparison
"Flammable" means something can catch fire or burn easily. It is the preferred word on safety warnings because it is unambiguous.
Do not store flammable liquids near open flames or heat sources.
The building was evacuated because of a flammable gas leak in the basement.
Always check whether a cleaning product is flammable before using it near the stove.
"Inflammable" means exactly the same as "flammable": that something catches fire easily. It is not the opposite. The "in-" prefix here comes from Latin and does not negate the word.
Warning: inflammable materials must be kept away from any source of ignition.
Old buildings were often constructed with inflammable materials that made fires difficult to control.
The situation had become highly inflammable, any spark could trigger a violent reaction.
Common mistake
- •Dangerous error: assuming "inflammable" means it CANNOT burn (by analogy with "invisible" or "impossible").
- •Both words, "flammable" and "inflammable", mean exactly the same: can catch fire easily.
- •No material labeled "inflammable" is fire-safe.
Trick to remember it
- •The "in-" in "inflammable" is not negative: it comes from Latin "inflammare" (to set fire to), not from the negative prefix.
- •Same with "invaluable" (of immense value) and "infamous" (of bad fame).
- •Seeing "inflammable" means: danger, can burn.
Quick rule
- •"Flammable" and "inflammable" mean the same: can catch fire easily.
- •The correct antonym is "non-flammable" or "fireproof".
Did you know?
This vocabulary confusion was literally deadly: there were industrial accidents in the 20th century where workers believed "inflammable" meant "fire-safe", an interpretation that caused preventable fires. It was a concrete reason why industrial standards shifted toward "flammable" on warning signs. English is one of the few languages where the prefix "in-" can mean BOTH "into" (as in "inflammare") AND "negation" (as in "invisible"), creating potentially dangerous ambiguity.
Practise what you learned
Exercise 1 · Pick the right one
Keep this chemical away from flames. It is highly _____.
Exercise 2 · Pick the right one
Why do safety labels prefer "flammable" over "inflammable"?
Exercise 3 · Form the word
Related word pairs
'Loath' is the adjective meaning reluctant or unwilling; 'loathe' is the verb meaning to detest intensely.
"Sensual" = related to physical or sexual pleasure and desire; "sensuous" = pleasantly engaging the senses in an aesthetic way.
"Above" is at a higher level without contact; "over" implies covering, movement, or crossing.
'Currently' means 'at the present time'; 'actually' means 'in reality', not 'nowadays'.
Bryan López
Founder of SpeakUP Academy