The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

Which is why I'm naming you
new Master of Coin.
Game of Thrones Season 3, Episode 3

Well, I don't know what that is,
but it's got "COIN" in it,
The Big Bang Theory Season 11, Episode 9

kill it as she watches,
and pay for her pain with a silver COIN?
Game of Thrones Season 3, Episode 1

This is the COIN the slaver gave me
Game of Thrones Season 7, Episode 5

(COIN clinks in glass) Okay,
seriously, stop. What the hell?
The Big Bang Theory Season 5, Episode 19