Why do the words flammable and inflammable mean the same thing?
The dictionary at reference.com indicates that both words mean:
“easily set on fire; combustible.”
The prefix in- means not. The word roots section on membean.com says so. The page even has a cute little interactive tree with examples.
Call me crazy, but is seems to me that having two words that ought to have opposite meanings but don’t is just asking for trouble.
“Dude! That truck has a sign that says it’s inflammable!
Hold my beer and watch this!”
Not a good thing, unless you’re trying for a Darwin Award.