"What" is defined grammatically as an interrogative pronoun
... used interrogatively in asking for the specification of an identity, quantity, quality, etc. (Wiktionary)
In dictionaries, however, what is never defined semantically.
If I meditate on a word like car, I inevitably associate images, feelings and experience with the word. Even if I think of nothingness I somehow associate sensations and a mental image of emptiness (even if it may be wrong). When I contemplate the word who, I associate the word with a "person whose identity is unknown". When I think of what however, in terms of pragmatics, it seems to suggest a request for more information to the interlocutor, but semantically, I cannot find any meaning to it.
Hence this odd question:
What is the semantic meaning of what (or its equivalent in any language)? Could the meaning of what be defined as "a thing unknown to me"?