1 cave

2 hole

3 zero (unambiguous spoken form when spelling out numbers)

4 classifier: 个 gè

1 concave or convex

2 bumps and holes

3 uneven (surface)

4 rugged

1 recess

2 notch

3 groove

4 fillister

1 to cave in

2 hollow

3 sunken

4 depressed

1 tunnel

2 cave

3 burrow

4 dugout

1 A small hole not plugged will make you suffer a big hole (idiom); A stitch in time saves nine.

1 a small hole not plugged will give you grief when it gets bigger (idiom)

2 a stitch in time saves nine

1 If you don't plug the small hole, the big hole will be hard to repair (idiom); A stitch in time saves nine.

1 A small hole not plugged will make you suffer a big hole (idiom); a stitch in time saves nine

1 lit. to pull a snake from its hole

2 to expose a malefactor (idiom)