Kafir
Kāfir (Arabic: كافر; pl. كافرون, kāfirūn) is an Islamic term of Arabic origin used by Muslims to refer to non-Muslims who deny the God of Islam, reject his authority, or do not accept the message of Islam as truth. Kafir is often translated as 'infidel', 'truth denier', 'rejector', 'disbeliever', 'unbeliever', The term is used in different ways in the Quran, with the most fundamental sense being ungrateful towards God.