Apparently, Americans pronounce the word lieutenant as loo-ten-unt, but British people say lef-ten-unt. There are several different theories for why that's the case: some think it got confused with Germanic words or that people just misread the u as a v, but the Oxford English Dictionary dismisses these theories. According to it, changes like this are rare and it's "difficult to explain" but most likely has something to with the labio-velar approximant (a w sound) being pushed a little further back to become realized as a labio-velar fricative (f or v) in certain dialects. The word comes from Old French lieu tenant, which literally meant "place-holder" because lieutenants were considered substitutes for higher-ranking officers. Lieu, which is the same as in the phrase in lieu, comes from Latin locus, meaning "place", and tenant, which is the same as the English word for "occupant", comes from the Latin verb tenere, meaning "grasp".
Hello! I'm Adam Aleksic, a sophomore studying linguistics and government at Harvard University, where I founded the Harvard Undergraduate Linguistics Society. I also have disturbing interests in politics, vexillology, geography, board games, conlanging, and law.