vacant

adj. empty, unfilled; unoccupied; not in use; lacking expression; (Law) withno tenant and empty of furniture; not claimed (e.g. an inheritance)

Occupancy is a defined legal term in building construction and building codes. It refers to the use or intended use of a building or part thereof for the shelter or support of persons, animals or property. A closely-related meaning is the number of units in such a building that are rented or leased, or otherwise in-use. The lack of occupancy in this sense is a vacancy.
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Adjective
1. void of thought or knowledge; "a vacant mind"
(similar) empty
2. without an occupant or incumbent; "the throne is never vacant"
(similar) empty

adj. vacant, unoccupied, void

adv. vacantly, in a vacant manner

adj. vacant, empty, unfilled