Broadcast a lunatic marine (8)
I believe the answer is:
nautical
'marine' is the definition.
('nautical' can be a synonym of 'marine')
'broadcast a lunatic' is the wordplay.
'broadcast' indicates an anagram.
'a'+'lunatic'='alunatic'
'alunatic' anagrammed gives 'NAUTICAL'.
(Other definitions for nautical that I've seen before include "Marine" , "Maritime" , "Of sailors or ships" , "about boats" , "Relating to sailors" .)