Why do “flammable” and “inflammable” mean the same thing, or is there a difference?

Question

Edit: SERIOUSLY, THANK YOU—

BTW my confusions stems from them having the same meaning online

Flammable: “easily set on fire”
Inflammable: “easily set on fire”

Definitions from Oxford Languages

In: Other

Answer 1

As it’s been mentioned the prefix in has two different meanings. To understand you need to understand the etymology of these words. I’ll try to keep it eli5:

First of all, let’s set forth the English definitions.

Flammable = easily set on fire.

Nonflammable = not easily set on fire.

Inflammable = flammable. Now, some dictionaries or people/professions may say it means nonflammable but that’s a modern re-defining of it so I will ignore that for this.

There are two Latin words at the heart of this all. In Latin, flammāre (flammō among other conjugated forms) means to set on fire (from flamma for flame). Inflammāre is a synonym in Latin, maybe with a more “doing” connotation because of the in- prefix. So, both of these mean to set on fire in Latin.

The English word inflammable is from the Latin inflammāre simply using the English -able suffix which makes something an adjective that can be done. So, is set on fire-able.

Flammable is a back-formation of inflammable to prevent confusion. Why? Because in Latin, the in- prefix has 2 meanings. One, in the “doing at” connotation as in inflammāre. Two, a “not” connotation as in for example infīnītus (where we get infinite), aka not fīnītus (finite).

Finally, nonflammable is simply an English compound from flammable, using the prefix non which means not. So, not flammable (or not inflammable, whatever floats your boat).