For listeners, remained formal (5)
I believe the answer is:
staid
'formal' is the definition.
(I've seen this in another clue)
'for listeners remained' is the wordplay.
'for listeners' shows a homophone (sound like).
'remained' becomes 'stayed' ('stay' can be a synonym of 'remain').
'stayed' is a homophone of 'STAID'.
(Other definitions for staid that I've seen before include "Sedate, sober" , "Very conventional and dull" , "Conventional (character)" , "Stuffy, traditional" , "Grave, sedate" .)