What is the word for using one part of speech where another would be more grammatical?

There's a Greek word that means using the wrong part of speech somewhere in a sentence, as in:

I don't know the who or the how or the when.

Where "who", "how", and "when" are being used for nouns. What's the word for this?

Solution 1:

The word you're looking for is anthimeria, artfully using a different part of speech to act as another in violation of the normal rules of grammar.

This switch might involve treating a verb like a noun, or a noun like a verb, or an adjective like a verb, and so on. Nancy Sinatra's 1960s song These Boots Are Made for Walkin' has You keep lying when you ought to be truthing. . . . You keep saming when you ought to be changing, for example.

Linguists are much preoccupied with e. e. cummings "he sang his didn't, he danced his did."