Book on anaesthetics? (7)
I believe the answer is:
numbers
I believe this is a double definition.
'book' is the first definition.
(I've seen this before)
'anaesthetics?' is the second definition.
(things that make things numb)
'on' is the link.
(Other definitions for numbers that I've seen before include "Old Testament book -- narcotics?" , "They subdue the pain" , "anaesthetists?" , "Biblical book - anaesthetics" , "quantity" .)