ingenious (adj.)

c. 1300, "mechanical device," especially one used in war; "manner of construction," also "skill, craft, innate ability; deceitfulness, trickery," from Old French engin "skill, wit, cleverness," also "trick, deceit, stratagem; war machine" (12c.), from Latin ingenium "innate qualities, ability; inborn character," in Late Latin "a war engine, battering ram" (Tertullian, Isidore of Seville). This is etymologically "that which is inborn," from in- "in" (from PIE root *en "in") + gignere "to beget, produce" (from PIE root *gene- "give birth, beget").

The sense of "device that converts energy to mechanical power" emerged in 18c. In 19c. the word was used especially of steam engines. Middle English also had ingeny (n.) "gadget, apparatus, device," directly from Latin ingenium.

1590s, "honor, nobility," from French ingénuité "quality of freedom by birth" and directly from Latin ingenuitatem (nominative ingenuitas) "condition of a free-born man," figuratively "frankness, generosity, noble-mindedness," from ingenuus "frank, candid, noble" (see ingenuous).

Etymologically, this word belongs to ingenuous, but in 17c. ingenious "intellectual, talented" and ingenuous so often were confused (even by Shakespeare) that ingenuity in English has come to mean only "capacity for invention or construction." That sense of this word is first attested 1640s; the word for it in Middle English was ingeniosity (the native word is craftiness). French ingénuité, meanwhile, has evolved through "natural and graceful freedom of manners" to "graceful simplicity" (compare ingenue); for the sense "ingeniousness," French uses ingéniosité.