Yours, Etc.: Origins and Uses of 8 Sign-Offs
1590s, "honor, nobility," from Middle French ingénuité and directly from Latin ingenuitatem (nominative ingenuitas) "condition of a free-born man," figuratively "generosity, noble-mindedness," from ingenuus (see ingenuous). Etymologically, this word belongs to ingenuous, but in 17c. ingenious and ingenuous so often were confused (even by Shakespeare) that ingenuity has acquired the meaning "capacity for invention or construction" (first attested 1640s).