On radio, remained calm and composed (5)
I believe the answer is:
staid
'calm and composed' is the definition.
(I know this)
'on radio remained' is the wordplay.
'on radio' shows a homophone (sound like).
'remained' becomes 'stayed' ('stay' can be a synonym of 'remain').
'stayed' sounds like 'STAID'.
(Other definitions for staid that I've seen before include "Proper; sedate" , "Serious or sober in character" , "Grave, sedate" , "Stiff; serious minded" , "Unadventurous, dull" .)