WordNet sense 1 (space that is surrounded by something):

enclosed space

WordNet sense 2 (soft decayed area in a tooth; progressive decay can lead to the death of a tooth):

caries, dental caries, tooth decay

WordNet sense 3 (a sizeable hole (usually in the ground)):

pit

WordNet sense 4 ((anatomy) a natural hollow or sinus within the body):

cavum, bodily cavity