Oh, thank heavens for the word flammable.
It means, obviously, something which can be set on fire; but how about inflammable? Will something inflammable burn or not?
I mean, ingenious means having genius; but inexpert means having no expertise.
I suppose, now I come to think about it (and it's only taken me about fifty years to sort this out) inflammable is the same word as inflamed, and something inflamed is hot to the touch. So inflammable means that, yes, it can be set on fire.
All the same, inflammable is a dangerously confusing word, and that's why everyone sensible uses flammable and non-flammable, instead.
Word To Use Today As Long As You Don't Mind No One Being Sure What You're Talking About And Are Prepared To Risk Things Going HorriblyWrong. Inflammable. This word comes from the Latin inflammere, which means to set on fire. The in bit looks as if it's the Latin in which means not, but actually it's the Latin in which means extra.
PS As a kid I was often told that imflammable was the opposite of inflammable, but hurray hurray, imflammable doesn't exist. It never has existed, either. And thank heavens for that.