Tiresome outside broadcast (7)
I believe the answer is:
tedious
'tiresome' is the definition.
(synonyms)
'outside broadcast' is the wordplay.
'broadcast' indicates anagramming the letters (letters scattered or cast around).
'outside' anagrammed gives 'TEDIOUS'.
(Other definitions for tedious that I've seen before include "Dull as ditchwater" , "Long, slow, dull" , "flat" , "Wearisome, boring" , "Humdrum" .)