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Flammable & inflammable

Posted by Bob on April 19, 2004

In Reply to: Flammable & inflammable posted by Jim on April 19, 2004

: Normally the prefix "in" means the opposite of the following word e.g. edible and inedible, direct and indirect, etc...

: Does anyone therefore know why flammable and inflammable mean the same thing?

: I'm wondering why there are two words for exactly the same thing. I wonder whether they originally meant easily set on fire and not able to be set on fire, but over time they were confused to mean the same thing.

From American Heritage Dictionary online:
Usage Note: Historically, flammable and inflammable mean the same thing. However, the presence of the prefix in- has misled many people into assuming that inflammable means "not flammable" or "noncombustible." The prefix -in in inflammable is not, however, the Latin negative prefix -in, which is related to the English -un and appears in such words as indecent and inglorious. Rather, this -in is an intensive prefix derived from the Latin preposition in. This prefix also appears in the word enflame. But many people are not aware of this derivation, and for clarity's sake it is advisable to