Definition from macmillandictionary.com
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He was accused of selling business secrets to competitors.
I can’t tell you what she said – it’s a secret.
Your secret is safe with me (=I will not tell anyone).
The secret is out (=everyone knows about it).
It cannot remain a secret much longer.
Can you promise to keep a secret?
Mandela kept his work a secret from the prison authorities.
Listen, I’ll let you in on a little secret.
What secrets of the universe will the new telescope reveal?
She always looks so slim – I wish I knew her secret.
The secret is always to warm the pot before putting in the tea.
The secret of our success is having highly skilled staff.