It took me eighteen years to learn that a fiancé is different from a fiancée; apparently the one with one e refers to men and the one with two refers to women. The words were borrowed in the middle of the nineteenth century from French, both going back to the Old French verb fiancer, meaning "to betroth". The root of that is fier, meaning "to trust", and -ance was just a suffix to form nouns. Earlier, in Latin, fier took the form of fidus, which could also mean "faithful" or "loyal", and that's reconstructed as deriving from a Proto-Italic word, feithos, which would be from Proto-Indo-European beyd, also "trust". Usages of both the words fiance and fiancee in English literature over time reveals that they peaked in utilization in the late 1990s for some reason and that most people spell them without the diacritics.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.