Usage patterns
〈事〉を密かに計画するto secretly plan something
They were secretly planning a new business venture.
密かな〈物〉a secret (ambition, hope, love, etc.)
She had a secret ambition.
密かに〈動詞〉to do something secretly, in private
He was secretly thinking of her.
〈人〉に密かな期待を寄せるto secretly place one's hopes in someone
The coach was secretly placing his hopes in the young player's talent.