I was discussing with a Christian friend of mine the authenticity of the Holy Qur'an, and I explained to him that without a shadow of a doubt that the Qur'an has been maintained word for word since it was delivered to us by the Prophet Muhammad (PBUH).
So he replied to me, that "assuming the Qur'an is authentic, how do we know that the meaning of the Arabic words and language hasn't changed?"
I got stuck. I am aware that it would be difficult to change due to the context clues of the most common words, but I wasn't able to give him a good answer?
I am even aware that are debates of meaning of specific verses such as in Surat At-Tariq [86:7]
Emerging from between the backbone and the ribs.
As opposed to the other translation that says:
Emerging from between the backbone and the loin.
The explanations of the language are written in the language, how could I have explained to him how we know that the language as a whole hasn't changed? Thanks.
EDIT: I must clarify that I am well aware that spoken Arabic has changed in meaning, my question is in reference to word by word meaning of the Qur'anic Arabic.