Why do the words "flammable" and "inflammable" mean the same thing?

That is because the prefix "in-" is in this case NOT the Latin negative prefix in- (related to the English prefix "un-" and which appears in words like "indecent" and "inglorious"). It is instead derived from the Latin preposition in, which means "in" and appears in words like "inflame."

That's a great question! It caused me to stop and do a search. I guess this is as good an explanation as any
https://www.merriam-webster.com/words-at-play/flammable-or-inflammable

Might be like famous and infamous

Just seen that on Dawson’s Creek & I have no idea lol 🤷🏻‍♀️

the words are getting shorter! 😯

Now that is a tricky one.lol

😮

One is the act, inflammable. The other is a possibility, flammable.

You’re not supposed to ask these questions! It makes the natives restless. Bullshit is the glue holding all the other bullshit together. So please please please cease and desist. I will tell them not to knock on your door for a “discussion.” OK? I’m going to smile now. You smile and nod and we will pretend to laugh. 😃