flammable v. inflammable v. nonflammable

Flammable means ‘able to ignite and burn easily’. The Latin prefix in- means ‘not’, and can be found in such words as inadequate and incredible. This would lead you to believe that inflammable means ‘not flammable’. However, there is another prefix, en-, which is used as an intensive in words like entangle. En- can also take the form em-, or, in this case, in-, depending on the word it precedes. So, inflammable just means ‘flammable’. The word for something that isn’t readily burned is nonflammable.

Jack Lynch on flammable .v inflammable v. nonflammable