Why do flammable and inflammable mean the same thing? Isn't it kind of weird?
donald remero [ Moderator ]
"Inflammable" is the older word, which dates to 1605. Inflame actually enters the language in the 14th century along with the root noun, "flame," by way of French influence. Flammable actually dates only to 1813.
I think it is safe to assert that the prefix began to be dropped because of the ambiguity that the prefix "in-" causes in being used as an intensifier (from the Latinate meaning of "into," or in English "en-") as opposed to a negator as it is more commonly used, being derived from the (often) homophonic Old English "un-".
The Middle English word actually is "enflamen" with "en-" instead of "in-", and it is the same in French. But in Latin, it is an "in-".
Answering the real question about why "inflammable" does not mean "non-flammable" has to do with the inherent ground for confusion among the Old English "en-" and the Latinate "in-" and the Old English "un-" which depending on dialect, any two or all three might be virtually in/un-distinguishable. We just never figured out how to en-distinguish them clearly and consistently.