Secretly

偷偷

Secretly, Stealthily, Surreptitiously

暗中

In, Secretly

暗自

Implicitly, Inwardly, Quietly, Secretly, To

祕密

Secret, Secretly, Surreptitiously

私自

Personally, Privately, Secretly

暗地裡

Secretly

祕密地

Secretly, Surreptitiously

背地裡

Behind, In, Secretly