Keep it under your hat?

[rumba]

Test No. incompl/advan-41 "Talking through his hat", question 4

I hope you can keep a secret because I'd like you to keep this information ......... your hat.

(a) under
(b) in
(c) by
(d) over

Test No. incompl/advan-41 "Talking through his hat", answer 4

I hope you can keep a secret because I'd like you to keep this information under your hat.

Correct answer: (a) under

Your answer was: correct
_________________________

What does it mean?
under your hat

[Torsten]

If you keep something under your hat, you keep it secret, confidential and don't tell anybody about it.

TOEIC listening, talks: Reporting on a company's stock price movements