A Stradivarius is a violin — or sometimes a viola or cello — made by Antonio Stradivari, an Italian maker who worked in the town of Cremona and died in 1737. Players believe his instruments sound better than any made since, and only about 500 or so survive, so one can sell for millions of US dollars. Because of that, the word has stopped being only a name. It is a capital-letter noun for a thing, like Kleenex or Toyota, and you can say 'a Stradivarius' or 'two Stradivariuses'. People shorten it to a Strad when they are being friendly about it. And it has become a way of saying 'the finest example there is' — someone might call a certain camera the Stradivarius of cameras. Though actually the sound part is not as settled as people say. Careful tests where listeners cannot see the instrument have often failed to show that a Stradivarius beats a good modern violin. So a teacher should be honest here: the price and the fame are real facts, and the magic sound is a belief that many players hold strongly but that science has not confirmed.