c. 1400, "physical, human, mortal," from Old French carnal and directly from Latin carnalis "fleshly, of the flesh," from carnis "of the flesh," genitive of caro "flesh, meat," "flesh," originally "a piece of flesh," from PIE root *sker- (1) "to cut."
Meaning "sensual, pertaining to the passions and appetites of the flesh" is from early 15c.; that of "worldly, sinful, not spiritual" is from mid-15c. Carnal knowledge "sexual intercourse" is attested from early 15c. and was in legal use by 1680s. Medieval Latin carnalis meant "natural, of the same blood," a sense sometimes found in Middle English carnal.