Justification for an affair? (8)

I believe the answer is:

occasion

This clue is a double definition.

'justification' is the first definition.
(thesaurus)

'for an affair?' is the second definition.
('occasion' can be a synonym of 'affair')

(Other definitions for occasion that I've seen before include "Opportunity" , "incident" , "Provoke" , "Time of (maybe special) event" , "Give rise to" .)

I've seen this clue in the Evening Standard.

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