A case of justification (7)

I believe the answer is:

defence

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'justification' is the definition.
(I know that defence is a type of justification)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for defence that I've seen before include "Protection from danger" , "Protection; justification" , "Armed forces' role" , "Case for the accused" , "Military's purpose" .)

I've seen this clue in the Evening Standard.

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