Well, I guess this is a topic I’ll constantly add to. So this is only the beginning, and as someone who’s very interested in languages, I am out hunting for Americanisms all the time. One thing is certain: it’s English, but very often, it feels like it’s nothing to do with English at all. And there are tons of words that sound like they mean one thing only to actually mean something completely different. Of those, a few examples are:
Football: It has nothing to do with a ball (it’s played with an egg shaped thingy), and you don’t actually ever use your feet to play it.
Entree: This is a French word meaning “appetizer”, or “starter”. In America, it means “main course”.
Marinara (as in marinara sauce): This is an Italian word meaning “of the sea”, as in Pizza Marinara is pizza with seafood. In America, this is a plain tomato sauce you can have with pretty much anything from pizza to pasta. Not a hint of fish.
Of course, I also have to take into consideration the fact that California (and Californian American) is very different to the rest of the States, and, as many Americans will confirm, should be its own country. If you’re interested, have a read through the development of Californian English, with a few audio examples to listen to. If you click on the link with Dr. Penelope Eckert, you can hear what Elise might sound like one day (I really hope not).