confidentially
adv. 秘密地；作为心腹话地
例句
She told me confidentially that she is going to retire early.
她私下告诉我她要提早退休。
《牛津词典》
Confidentially, I am not sure that it wasn't above their heads.
私下里说，我不确定这没有超出他们的理解。
《柯林斯英汉双解大词典》
Nash hadn't raised his voice, still spoke rather softly, confidentially.
纳什没有提高嗓门，仍然很轻地、悄悄地说。
