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.

And if I have to watch him squeeze into
an Ewok COSTUME, so be it.
The Big Bang Theory Season 10, Episode 17

"Where's your COSTUME?
Why are you wearing work clothes?"
The Big Bang Theory Season 6, Episode 5

Yeah, so the judges can give out
the prizes for best COSTUME.
The Big Bang Theory Season 1, Episode 6

He didn't remember me, because the last
time we met I was in a Halloween COSTUME.
The Big Bang Theory Season 2, Episode 14

PRIYA: I can\'t believe I\'m wearing
my brother\'s Halloween costume.
"
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PRIYA: I can\'t believe I\'m wearing
my brother\'s Halloween costume.
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PRIYA: I can't believe I'm wearing
my brother's Halloween COSTUME.
The Big Bang Theory Season 4, Episode 24