Correct

私底下

/ sīdǐxia /
Strokes

Definition

privately/secretly/confidentially

Example

As an Adverb

in private/secret/confidence; privately; secretly

1
xiǎng
xia
私底下
tántán
谈谈
  

I wish to talk with him privately. /I wish to talk with him in private.

2
shì
biéren
别人
xia
私底下
gào
告诉
de
  

I was told about that matter in secret.

3
Zài
xia
私底下
shuō
huàihuà
坏话

speak ill of sb behind one's back

4
xia
私底下
tiáojiě
调解

mediate in private