early 15c., "intellectual, talented," from Old French ingenios, engeignos "clever, ingenious" (Modern French ingénieux), from Latin ingeniosus "of good natural capacity, full of intellect, clever, gifted with genius," from ingenium "innate qualities, ability; inborn character," literally "that which is inborn," from in- "in" (from PIE root *en "in") + gignere "to beget" (from PIE *gen(e)-yo-, suffixed form of root *gene- "give birth, beget").

Sense of "skillful, crafty, clever at contrivance" first recorded 1540s; earlier in this sense was Middle English enginous (mid-14c.), from Old French engeignos. Middle English also had engineful "skillful (in war)" (c. 1300). By a direct path, Latin ingenium produced Middle English ingeny "intellectual capacity, cleverness" (early 15c.), but this is obsolete. Compare engine. Related: Ingeniously; ingeniousness.

"young woman who displays innocent candor or simplicity," 1848, from French ingénue "artless girl," especially as a character on the stage, noun use of fem. of ingénu "ingenuous, artless, simple" (13c.), from Latin ingenuus "frank, upright, candid," originally "free-born" (see ingenuous). Italicized in English into 20c.

1590s, "noble in nature, high-minded; honorably straightforward," from Latin ingenuus "with the virtues of freeborn people, of noble character, frank, upright, candid," originally "native, freeborn," literally "born in (a place)," from in- "in" (from PIE root *en "in") + PIE *gen(e)-wo-, suffixed form of root gene- "to give birth, beget, produce" (see genus). Sense of "artless, innocent" is 1670s, via evolution from "honorably open, straightforward," to "innocently frank." Related: Ingenuously; ingenuousness.

c. 1300, "free, liberal, generous;" 1540s, "outspoken," from Old French franc "free (not servile); without hindrance, exempt from; sincere, genuine, open, gracious, generous; worthy, noble, illustrious" (12c.), from Medieval Latin francus "free, at liberty, exempt from service," as a noun, "a freeman, a Frank" (see Frank).

Frank, literally, free; the freedom may be in regard to one's own opinions, which is the same as openness, or in regard to things belonging to others, where the freedom may go so far as to be unpleasant, or it may disregard conventional ideas as to reticence. Hence, while openness is consistent with timidity, frankness implies some degree of boldness. [Century Dictionary]

A generalization of the tribal name; the connection is that Franks, as the conquering class, alone had the status of freemen in a world that knew only free, captive, or slave. For sense connection of "being one of the nation" and "free," compare Latin liber "free," from the same root as German Leute "nation, people" (see liberal (adj.)) and Slavic "free" words (Old Church Slavonic svobodi, Polish swobodny, Serbo-Croatian slobodan) which are cognates of the first element in English sibling "brother, sister" (in Old English used more generally: "relative, kinsman"). For the later sense development, compare ingenuity.