1》 [ interrogative pronoun ] what or which person or people.
2》 [ rel. pronoun ] introducing a clause giving further information about a person or people previously mentioned.
↘ archaic the person that; ~ever.
OE hwā , of Gmc origin.
According to formal grammar, ~ forms the subjective case, while ~m forms the objective case and so should be used in object position in a sentence. In modern English there are many speakers ~ rarely use ~m at all, employing ~ in all contexts; today this use is broadly accepted in standard English.