Channel broadcast, say, true (7)
I believe the answer is:
estuary
'channel' is the definition.
(thesaurus)
'broadcast say true' is the wordplay.
'broadcast' indicates anagramming the letters.
'say'+'true'='saytrue'
'saytrue' is an anagram of 'ESTUARY'.
(Other definitions for estuary that I've seen before include "River outlet" , "a sort of English" , "should be apparent at Dartmouth?" , "Wide part of a river where it meets the sea" , "Accent that's been spreading out from London" .)