Answer:

anesthesia

Answer	Crossword Clue
ANESTHESIA	Operating room number?
ANESTHESIA	Cause of senselessness
ANESTHESIA	It can knock you out

ANESTHESIA	Unconscious state
ANESTHESIA	Operator's number?
ANESTHESIA	"Feeling no pain" state
ANESTHESIA	Temporary dullness of perception.
ANESTHESIA	Sleep of a sort.
ANESTHESIA	Operating-room process
ANESTHESIA	Loss of feeling
ANESTHESIA	What nitrous oxide produces

ANESTHESIA	Number of people
ANESTHESIA	Number of folks?
ANESTHESIA	Surgical tool
ANESTHESIA	Loss of bodily sensation