Quiz: Remember the definition of mal de mer?
1590s, "natural, not acquired," from Latin genuinus "native, natural," from root of gignere "beget" (see genus), perhaps influenced in form by contrasting adulterinus "spurious." [Alternative etymology is from Latin genu "knee," from a supposed ancient custom of a father acknowledging paternity of a newborn by placing it on his knee.] Meaning "really proceeding from its reputed source" is from 1660s. Related: Genuinely; genuineness.