1 : having nothing inside : not solid

• a hollow log

2 : curved inward or down

• hollow cheeks
• There was a hollow spot in the field.

3 : not having real value or meaning

• They achieved a hollow victory over a team missing its best players.
• She made hollow
• Their threats ring hollow. = Their threats have a hollow ring.

4 : Note — A sound that is hollow is like the sound made when you hit something that is empty inside.

• He heard a hollow sound when he knocked on the wall.

5 : weak and without any emotion

• “It’s useless,” he said in a hollow voice.
• a hollow laugh

hollowly adverb /ˈhɑləli/

• “It’s useless,” he said hollowly.

hollowness noun [noncount]

• the hollowness of her promises