Say in your case you have nothing to hide (7)
I believe the answer is:
declare
'say' is the definition.
(declaring is a kind of saying)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for declare that I've seen before include "State emphatically" , "... cut short innings" , "Make a statement, to customs perhaps" , "Make clearly known" , "Aver, state" .)