Engañar is the common Spanish word meaning “to deceive”, and is especially common in its meaning of “to cheat on [a spouse or girl/boyfriend].”
But who would have thought its related to the English ingenuous?
Both are, after all, forms of naïveté.
Both come from the Latin root gen‑, meaning “to produce”. Think, genesis. After all, in the beginning, everything and everyone was naive.
Via the Greek parallels and Latin descendants, we get a myriad of modern words, including: genus and genius. There is a certain genius in deceiving. Of course.