Red Maxim broadcast on radio (4)
I believe the answer is:
sore
'red' is the definition.
(thesaurus)
'maxim broadcast on radio' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is present in the answer.
The remaining letters 'so' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sore that I've seen before include "To be very old" , "Raw place (on the body)" , "Bruised" , "Painful - resentful" , "Painful, or the source of pain" .)