precarious

adj. /prɪˈkeriəs/ C1

不稳固的；危险的

Not safe or certain; dangerous and likely to fall.

仙境例句

The books looked precarious on the well's shelf; one touch could bring them all down.

井壁书架上的书看着摇摇欲坠，碰一下就可能全掉下来。