K-P-R is a Semitic root, in Arabic and Hebrew rendered as K-F-R (Arabic: ك-ف-ر; Hebrew: כ-פ-ר).
The basic meaning of the root is "to cover", but it is used in the sense "to conceal" and hence "to deny", and its notability derives from its use for religious heresy or apostasy (as it were describing the "concealment" of religious truth) in both Islam and Judaism.
Georges Bohas and Mihai Dat, in a study of triconsonantal Semitic roots, noted a connection of X-p-r, p-r-X and p-X-r roots (where X is another consonant) with meanings like "break off", "part," "cut", "shut off", "remove", "break up", "hide", "expel", suggesting a Proto-Semitic biconsontal root pr meaning "cut, divide."[1] It is first attested in the Akkadian verb kaparu ("wipe, smear"), with D-stemkupparu.[2]
Kāfir (Arabic: كافِر), pl. Kuffār (كُفّار) and Kāfirīn (كافِرين), Kofer (Hebrew: כופר), pl. Kofrim (Hebrew: כופרים) — "coverer" — unbeliever; "a person who hides or covers the truth"