كافر
Kāfir
One who rejects or denies the truth; literally, one who covers it up.
What it means
The root k-f-r means “to cover”. The Quran uses a related word for farmers, who cover seed with soil (57:20). As a religious term it describes a person who knows the truth and hides or rejects it, and it is a statement about belief, not a name for a people.
Chapter 109 ends “to you your religion, and to me mine”. The Quran does not forbid kindness and justice to those who do not fight Muslims over religion, and it says God loves those who act justly (60:8).
Often misunderstood as
That it is a slur, or a licence to kill anyone who is not a Muslim.
What the sources say
The decision about who has rejected God is left to God. A hadith in Sahih al-Bukhari warns that if a man calls his brother “kafir”, one of them has earned the word, and jurists accordingly forbade accusing Muslims of disbelief lightly. The Quran also gives separate words for the People of the Book and for polytheists, and does not use one label for all.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 45, listed as KĀFIR. The definition is restated here.