Raid spoiled by old medium (5)
I believe the answer is:
radio
'medium' is the definition.
(I know that radio is a type of broadcasting)
'raid spoiled by old' is the wordplay.
'spoiled' is an anagram indicator.
'by' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'raid' with letters rearranged gives 'radi'.
'radi'+'o'='RADIO'
(Other definitions for radio that I've seen before include "Marconi invented it" , "Communications medium" , "It used to be called the wireless" , "Receiving set" , "broadcasting station" .)