Correct

密室

/ mìshì / 
Strokes

Definition

a room for keeping sth hidden/secret room/hidden chamber

Example

As a Noun

backroom; secret room

1
Huìyì
会议
zài
在
mìshì
密室
lǐ
里
jìnxíng
进行
  
。

The meeting was held behind closed doors.