Answer (by Tariq Mahmood Hashmi)

The word kafir is a derivation of the verb kafara which, in Arabic, means to cover, to reject, to be ungrateful. Now there are various stages of rejection. The Qur'an refers to the polytheists who lived before the Prophet sws as kafir. The Almighty says: And when a book came to them from God, confirming the prophecies, they have with them- while they used to pray for victory over the rejecters [kāfirūn]- and, when that came to them, which they recognized, they rejected it. So, God’s curse be on these rejecters. (2:89)

Then there are those who reject the message on the basis of some arguments. The term is also applied to the people who reject truth, Messenger and His claims, after all the signs and arguments are presented to them in ultimate form. In this sense the Qur'an may also refer to them as al-kafiroon. It tells us that they would not believe even after reality is put bare before their eyes. It is the context in which the term is applied which helps us understand in which sense the word is being used.