Old anaesthetic one brought in - no matter which (6)
I believe the answer is:
either
'no matter which' is the definition.
Both the definition and answer are adverbs. Perhaps they are linked in a way I don't understand?
'old anaesthetic one brought in' is the wordplay.
'old anaesthetic' becomes 'ether' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'brought in' indicates putting letters inside.
'ether' placed around 'i' is 'EITHER'.
Can you help me to learn more?
(Other definitions for either that I've seen before include "Word introducing first alternative" , "No matter which (of two)" , "Her tie (anag.)" , "Word indicating the following alternatives" , "One of two alternatives" .)