Serious-minded listener has a comfortable retreat (7)
I believe the answer is:
earnest
'serious-minded' is the definition.
(I've seen this before)
'listener has a comfortable retreat' is the wordplay.
'listener' becomes 'ear' (body part which hears or listens).
'has' says to put letters next to each other.
'a comfortable retreat' becomes 'nest'.
'ear'+'nest'='EARNEST'
(Other definitions for earnest that I've seen before include "Serious - money deposit" , "See 1" , "Art deserving" , "Showing sincere and intense conviction" , "'Serious, sincere (7)'" .)