flammable vs. inflammable

Inflammable or flammable? There is no difference in meaning between these two words, but flammable is now the preferred choice in both British and American English.

Inflammable is the original form, derived from the verb inflame. But as the in- is easy to interpret as the common negative prefix in- (e.g., as in inescapable, invulnerable, inorganic), the word has always caused confusion. Because this is a rare case of word confusion that can have dangerous real-world consequences, a change was inevitable—particularly once the Industrial Revolution made inflammable materials much more common.

The less confusing flammable began to enter common usage in the early 19th century. That version has grown in prominence ever since, and it is now more common. But you can still get away with using inflammable, especially as it is still sometimes seen in warnings on things like gas cans and cleaning products.

Although inflammable is fading into the past, inflame and inflammatory are not going anywhere.