Dull outside broadcast (7)
I believe the answer is:
tedious
'dull' is the definition.
(I know that dull can be written as tedious)
'outside broadcast' is the wordplay.
'broadcast' is an anagram indicator (letters scattered or cast around).
'outside' anagrammed gives 'TEDIOUS'.
(Other definitions for tedious that I've seen before include "Banal" , "Wearisome, boring" , "Dull as ditchwater" , "Long, slow, dull" , "not worth listening to?" .)