Illogical English #8

indecent is opposite of decent
inescapable is opposite of escapable

We all know that “incorrect” means “not correct”, and that “indirect” means “not direct”. So, what does “inflammable” mean? Surely, it would logically mean “not flammable”, but in fact both words mean the same thing – easy to catch fire.
“Flammable” manes “inflammable”.