[noun] a cavity or space in something; "hunger had caused the hollows in their cheeks"
[noun] a small valley between mountains; "he built himself a cabin in a hollow high up in the Appalachians" Synonyms:holler
[noun] a depression hollowed out of solid matter Synonyms:hole
[verb] remove the inner part or the core of; "the mining company wants to excavate the hillsite" Synonyms:excavate, dig
[verb] remove the interior of; "hollow out a tree trunk" Synonyms:out, core out
[adjective] 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"