Three for anaesthetic (5)
I believe the answer is:
ether
'for anaesthetic' is the definition.
(ether is a kind of anaesthetic)
'three' is the wordplay.
'three' can be anagrammed to 'ETHER'.
But, I am not sure how this is indicated.
Can you help me to learn more?
(Other definitions for ether that I've seen before include "Liquid used as anaesthetic/ solvent" , "An early anaesthetic" , "Colourless volatile highly inflammable liquid" , "It could knock you out" , "Formerly an anaesthetic" .)