Quran's Arabic
It is beyond question to consider that Quran used words which are not in the vocabulary or use of Quraish. There is no way to to claim that Quran used such words which originated in the dialects of other arabic tribes and they were not the part of the language spoken by Quraish. Quran meant to address Quraish, in a clear language. The most authentic source of the language of Qurish is Quran itself. It asked them if they had doubt about it being conceived by Muhammad (PBUH) bring its like.