ひそ密hisoかkaひそ秘hisoかka
1.
An action or situation that occurs discreetly without the awareness of others, emphasizing a sense of secrecy or concealment.
2.
A manner of engaging in activities or experiences that are meant to remain undisclosed or hidden, often for personal enjoyment or private delight.
3.
The act of doing something in a covert or stealthy way, with the intention of keeping it hidden from outside scrutiny or knowledge.
Example:
彼はひそかにあなたの財産を狙っていますよ。