ingenuity

1590–1600; < Latin ingenuitās innate virtue, etc. (see ingenuous, -ity); current senses by association with ingenious

Ingenuity comes to English straight from Latin ingenuitās “condition or status of being a freeborn person,” and also “the qualities befitting a freeborn person, nobility of character, honesty, modesty, frankness” (note that these meanings pertain to legal status or citizenship and then to the civic virtues implied by ingenuitās, the implicit assumption being that a person of free birth was more likely to be honorable). Ingenuitās is a derivative of the adjective ingenuus “native to a place, indigenous, born of a free father, freeborn, having the qualities of a freeborn person,” which is what the English derivative ingenuous used to mean. Latin ingenuus, whose literal meaning is “born in,” is composed of the preposition and prefix in, in- and the verb gignere “to beget, give birth to.”
Ingenuity formerly had the meaning “simplicity, candor, frankness,” which corresponds to the current meaning of ingenuous, an adjective which comes directly from Latin ingenuus. Ingenuity with the sense “cleverness, inventiveness, skill” is the result of the mutual confusion— conflation is perhaps the better word—of the adjective ingenious with ingenuous, evidence of which can be found in literature of the 17th and 18th centuries. Ingenious comes from the Latin adjective ingeniōsus “intelligent, talented, clever, gifted,” derived from the noun ingenium “natural disposition, (good) mental abilities, talents, or powers (that is, personal temperament and intellectual qualities).” Latin ingenium comes from the same elements, in, in- and gignere, as ingenuitās and ingenuus. From such similar roots, a confusion was born.