a small valley between mountains; "he built himself a cabin in a hollow high up in the Appalachians"
a cavity or space in something; "hunger had caused the hollows in their cheeks"
as if echoing in a hollow space; "the hollow sound of footsteps in the empty ballroom"
not solid; having a space or gap or cavity; "a hollow wall"; "a hollow tree"; "hollow cheeks"; "his face became gaunter and more hollow with each year"
the central part of a car wheel (or fan or propeller etc) through which the shaft or axle passes
a center of activity or interest or commerce or transportation; a focal point around which events revolve; "the playground is the hub of parental supervision"; "the airport is the economic hub of the area"