hidden

the use of hidden cameras.隐藏式摄像机的使用

Some areas can hold hidden dangers for dogs..一些区域可能对狗有隐伏的危险。

the hidden meaning behind his words.他的言外之意

Be on the lookout for hidden costs in hotel bills..小心酒店账单中有隐性收费。

hidden trouble,隐患

hidden danger,隐患

hidden curriculum,隐性课程；潜在课程；隐蔽课程；非正式课程

hidden line,隐藏线