Thorough, say (5)
I believe the answer is:
utter
I believe this clue is a double definition.
'thorough' is the first definition.
(I know that thorough can be written as utter)
'say' is the second definition.
(to utter something is to speak or say it)
(Other definitions for utter that I've seen before include "Perfect" , "Articulate, express" , "issue" , "Antique offer for sale" , "State - unqualified - rank" .)