From the Word IQ Encyclopedia
(This article is about the strait; Bosphorus is also a university in Turkey.)
The Bosporus or Bosphorus (Turkish Bo?aziçi) is a strait that separates the European part of Turkey from its Asian part, connecting the Sea of Marmara with the Black Sea. (...) Bosporus means "ox ford" or "ox passage"; the name comes from a Greek myth about Io's travels after Zeus turned her into an ox for her protection. (...)
It's pretty obvious, actually -- the Greek noun is Bosporos, which the Romans remade as Bosporus. "us" is a Latin noun ending (like in "stylus", or "status" -- not "stylous", or "statous"; whereas "ous" is an ending suggesting an adjective; it is the English remake of the French "eux", like in "glamoureux" for example -- thus "glamorous".)
--What is it?
--What styluses are these?
--Them are the glamorous ones.
Once you get the sense of it, it's truly hard to get confused here.