Blur lost on radio (4)
I believe the answer is:
mist
'blur' is the definition.
(thesaurus)
'lost on radio' is the wordplay.
'lost' becomes 'missed'.
'on radio' indicates a 'sounds like' (homophone) clue.
'missed' sounds like 'MIST'.
(Other definitions for mist that I've seen before include "Obscure" , "Cloud; thin fog" , "Thin layer of fog" , "Think fog or low cloud" , "low-level cloud" .)