A form of assurance (6)

I believe the answer is:

policy

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'assurance' is the definition.
(thesaurus)

I don't understand the rest of the clue.

(Other definitions for policy that I've seen before include "Rules" , "Set of principles - plan" , "Honesty is said to be the best one" , "Plan of action - insurance document" , "(E.g. government) line" .)

I've seen this clue in The Globe and Mail.

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