1 cave

2 hole

3 zero (unambiguous spoken form when spelling out numbers)

4 classifier: 个 gè

1 ear

2 handle (archaeology)

3 and that is all (Classical Chinese)

1 a slap on the face

2 classifier: 记 jì

1 ear

2 classifier: 只 zhī

3 classifier: 个 gè

4 classifier: 对 duì

5 handle (on a cup)

1 headphones

2 earphones

3 telephone receiver

1 bowed head and ears glued (idiom); docile and obedient

2 at sb's beck and call

1 to block one's ears and not listen (idiom); to turn a deaf ear

1 lit. like thunder piercing the ear

2 a well-known reputation (idiom)

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