Yours, Etc.: Origins and Uses of 8 Sign-Offs
1790, from Arabic kafir "unbeliever, infidel, impious wretch," with a literal sense of "one who does not admit the blessings of God," from kafara "to cover up, conceal, deny, blot out." Technically, "non-Muslim," but in Ottoman times it came to be used almost exclusively for "Christian." Early English missionaries used it as an equivalent of "heathen" to refer to Bantus in South Africa (1792), from which use it came generally to mean "South African black" regardless of ethnicity, and to be a term of abuse since at least 1934.