Q: The word “whatever” is listed only as a pronoun in my dictionary, but don’t you think it’s also an adjective and an adverb in today’s language?
A: It depends on which dictionary you look it up in.
Merriam-Webster’s Collegiate Dictionary (11th ed.), for example, lists “whatever” as a pronoun (“I’ll eat whatever you cook”), an adjective (“He’ll take whatever terms you offer”), and an adverb (“I’m doing my best, whatever”).
Merriam-Webster’s says “whatever” has been used as a pronoun and an adjective since the 14th century.
As a pronoun, it means anything, everything, and no matter what. As an adjective, it means any or all that, no matter what, or of any kind at all.
The adverbial usage (meaning “in any case” or “at all events”) is more recent, but it’s almost a century and a half old, according to M-W.
The American Heritage Dictionary of the English Language (4th ed.) lists “whatever” as a pronoun and an adjective, but it describes as an interjection what Merriam-Webster’s calls an adverb “sometimes used interjectionally.”
Merriam-Webster’s treats all three usages as standard English. American Heritage generally agrees, though it describes as informal the pronoun use in a sentence like “Bring something to the party – pretzels, chips, whatever.”
The Oxford English Dictionary, however, considers the use of “whatever” as an adverb to be colloquial.
I think it’s OK to use “whatever” as a pronoun, an adjective, and an interjection (or an adverb used interjectionally, as M-W puts it), but let your ear be the judge. If the usage seems too casual, save it for speech or informal writing.