(n): a depression hollowed out of solid matter
(n): space that is surrounded by something
(n): an empty area (usually bounded in some way between things)
(n): soft decayed area in a tooth; progressive decay can lead to the death of a tooth
(n): the process of gradually becoming inferior
(n): (anatomy) a natural hollow or sinus within the body
(n): a particular complex anatomical part of a living thing
