Not even one more room?

Base- Vacant

Adjective meaning "not used," "not filled," or "not lived in."

Suffix- -Ancy

Suffix meaning "the state of" or "the result of."

Noun- Vacancy

Noun meaning "the state of being vacant." This can mean "a place that is not occupied," or "a job that is available."

So how can "vacant" become "vacancy" anyway?

"-Ancy" is a suffix that can be added to a base (in this case an adjective) to make it a new noun. This can turn a base from meaning "_____" to meaning "in the state of being ______" or "the result of being ________." We added "-ancy" to "vacant" to form "vacancy." A definition of "vacant" is "not lived in." A definition of "vacancy" is "the state of not being lived in."
The sign that stated that the hotel had vacancy loomed over the lonely, unoccupied room.