Hollow describes something having a void space inside; not solid. It can refer to physical objects that are empty within, or metaphorically to feelings, actions, or even people lacking substance, sincerity, or importance.
The sense of emptiness can convey a lack of fulfillment or depth, and the term can evoke a feeling of sadness, loneliness, or insincerity.
It can be a natural formation, created as a result of erosion or rot, or manufactured, to be able to hold something else.
DIG PIT DIP
DENT VALE DELL HOLE DALE
EMPTY
VALLEY CAVITY CRATER RECESS DIMPLE HOLLER SUNKEN
CONCAVE COREOUT VACUOUS
EXCAVATE
HOLLOWOUT INSINCERE
MEANINGLESS