interesting:

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 use only flammable to give
warnings.