[āo]
[形]
（比周圍低） concave; hollow; sunken; dented
full of bumps and holes; uneven
凹凸不平
The palm of one's hand is slightly concave.
人的手掌是微凹的。
[動]
（向內陷進去） cave in; dent; sink
The road caved in.
路凹下去了。
The car hood was dented in.
汽車的發動機罩已凹了進去。
His eyes [cheeks] have sunk in.
他的眼睛[面頰]凹下去了。