Hollow
Definition 1 of 4
Pro Tip 1/2
Physical emptiness
Use 'hollow' to describe objects that are empty on the inside, like tubes or boxes. She tapped the wall, looking for the hollow parts.
Pro Tip 2/2
Sound quality
'Hollow' can also describe a sound that echoes, as if coming from an empty space. The room's acoustics made her voice sound hollow.