Note that dictionaries document the (current, at the time of going to press) usage of language, they aren't authoritative. 'Correct' is what is in common usage and largely understood to be correct, even if that contradicts a dictionary (in which case the dictionary is probably out-of-date).

Who says it's not a word? Not a word, simply because lexicographers have not recognized it? When a lexicographer recognizes it, it has already been in use! Even Mr. Fiske says it is a word, although he obviously disprefers it.

I have become a dyed in the wool descriptionist because of Language Log, and have been known to cite entries here in battle against of the prescriptionistas of the Axis of Evil within the blogosphere.

Linguistic description is often contrasted with linguistic prescription