hollow
adjective /ˈhɒləʊ/
  /ˈhɑːləʊ/
Idioms - having a hole or empty space inside- a hollow ball/centre/tube/tree
- a hollow metal cylinder
- The tree trunk was hollow inside.
- Her stomach felt hollow with fear.
 Extra Examples- I felt hollow from lack of food.
- The experience left her feeling hollow and empty.
- I tapped the tin and it sounded hollow.
 
- (of parts of the face) sinking deeply into the face- hollow eyes/cheeks
- hollow-eyed from lack of sleep
 
- [usually before noun] (of sounds) making a low sound like that made by an empty object when it is hit- a hollow groan
 
- [usually before noun] not sincere- I've had enough of their hollow promises.
- She gave a slightly hollow laugh.
- Their appeals for an end to the violence had a hollow ring.
 
- [usually before noun] without real value- He won something of a hollow victory when his opponent was forced to withdraw with a serious injury.
 
Word OriginOld English holh ‘cave’; obscurely related to hole.
Idioms 
ring hollow/false 
- to give the impression of not being sincere or true- His expressions of support rang rather hollow.
- His promise rang hollow.
 
ring true/hollow/false 
- to give the impression of being sincere/true or not sincere/true- It may seem a strange story but it rings true to me.
- His expressions of support rang rather hollow.
- His promise rang hollow.