Certificate of insurance (6)
I believe the answer is:
policy
'certificate of insurance' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for policy that I've seen before include "(E.g. government) line" , "Plan of action of organisation - honesty is the best one" , "Course of action proposed in a political manifesto" , "Set of principles - plan" , "Honesty is said to be the best one" .)