I. adjective
1.
having a muffled or reverberating quality
had a deep hollow gloomy voice
Synonyms: cavernous, reverberant, sepulchral
Related Word: echoing, resonant, resounding, reverberating, sounding
Contrasted words: dead, dull, flat, toneless
2.
Synonyms: vain 1, empty, idle, nugatory, otiose
II. noun
1.
Synonyms: depression 2, basin, concavity, dip, sag, sink, sinkage, sinkhole
2.
Synonyms: hole 3, cavity, vacuity, void