Definition of vaults:
(n) :
An arched masonry structure supporting and forming a ceiling, whether freestanding or forming part of a larger building.
(n) :
Any arched ceiling or roof.
(n) :
(figuratively) Anything resembling such a downward-facing concave structure, particularly the sky and caves.
(n) :
Any cellar or underground storeroom.
(n) :
Any burial chamber, particularly those underground.
(n) :
The secure room or rooms in or below a bank used to store currency and other valuables; similar rooms in other settings.