volatile

adj. /ˈvɑːlətl/ C1

易变的；不稳定的

Likely to change suddenly and unexpectedly; easily evaporating.

仙境例句

The Queen's temper was volatile: smiling one minute, shouting “Off with his head!” the next.

王后的脾气说变就变：这一刻还在笑，下一刻就喊“砍掉他的头！”