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.

That is not the DEFINITION of professional.
The Big Bang Theory Season 2, Episode 14

That is the DEFINITION of conspiracy.
Game of Thrones Season 7, Episode 7

It's interesting but isn't ventriloquism
by DEFINITION a solo activity?
The Big Bang Theory Season 2, Episode 13

"A thief is, by DEFINITION,
an inveterate optimist.
Money Heist Season 1, Episode 4

I believe offering chocolate to someone
falls within the DEFINITION of "nice."
The Big Bang Theory Season 3, Episode 3