hidden
adjective [ usually before noun ] uk/ˈhɪd.ən/ us/ˈhɪd.ən/
(NOT EASY TO FIND)
B1 不易找到的，隐藏的
not easy to find
a hidden valley 一座不宜找到的峡谷
There were hidden microphones in the room to record their conversation. 房间内有隐藏的话筒记录他们的对话。
(NOT KNOWN ABOUT)
B2 不为人知的
that most people do not know about
hidden costs/taxes 隐匿成本／税收
Hidden problems may lead to an increase in costs. 预先不知道的问题可能导致成本的增加。