Definition of what :
1. As a relative pronoun
2. As an exclamatory word: - ( a) Used absolutely or independently; - often with a question following.
3. As an interrogative pronoun, used in asking questions regarding either persons or things; as, what is this? what did you say? what poem is this? what child is lost?
4. Something; thing; stuff.
5. Sometimes prefixed to adjectives in an adverbial sense, as nearly equivalent to how; as, what happy boys!
6. Used adjectively, equivalent to the . . . which; the sort or kind of . . . which; rarely, the . . . on, or at, which.
7. Used adjectively, meaning how remarkable, or how great; as, what folly! what eloquence! what courage!
8. Used adverbially in a sense corresponding to the adjectival use; as, he picked what good fruit he saw.
9. Used adverbially, in part; partly; somewhat; - with a following preposition, especially, with, and commonly with repetition.
10. Used substantively with the antecedent suppressed, equivalent to that which, or those [ persons] who, or those [ things] which; - called a compound relative.
11. Whatever; whatsoever; what thing soever; - used indefinitely.
12. Why? For what purpose? On what account?