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 I'm only saying "believe"
to sound MODEST,
The Big Bang Theory Season 5, Episode 21

Angela:
A MODEST proposition for you.
Westworld Season 2, Episode 3

My price would be MODEST.
Game of Thrones Season 1, Episode 7

I was being MODEST.
You got that, right?
The Big Bang Theory Season 11, Episode 11

about a boy of MODEST means
Game of Thrones Season 2, Episode 1