Listener to be found in snug right next door (7)
I believe the answer is:
nearest
'right next door' is the definition.
Both the definition and answer are adverbs. Perhaps you can see an association between them that I don't see?
'listener to be found in snug' is the wordplay.
'listener' becomes 'ear' (body part which hears or listens).
'to be found in' is an insertion indicator.
'snug' becomes 'nest' (I am not sure about this - if you are sure you should believe this answer much more).
'ear' put inside 'nest' is 'NEAREST'.
Can you help me to learn more?
(Other definitions for nearest that I've seen before include "Closest, being earnest" , "Stingiest" , "Most imminent - most mean" , "Most adjacent" , "Relations" .)