inflammable, noninflammable, flammable

The words flammable and inflammable mean the same thing. But the prefix in- misleads many people. They assume that inflammable means “not flammable” or “noncombustible.” This prefix (-in) is not the Latin negative prefix that appears in such words as indecent or inglorious. Instead, this prefix derives from the Latin preposition in and is an intensive prefix.

Many people are not aware of Latin prefixes, so for the sake of clarity, you should use flammable to give warnings.

The word nonflammable means that “something will not readily burn.”

Example: The tanker was clearly labeled “inflammable” because it was capable of carrying flammable substances. Fortunately, however, it was carrying nonflammable cooking oil when it overturned.