Brief: retain for matrimonial cases (6)

I believe the answer is:

inform

'brief' is the definition.
(I know that brief is a more specific form of the action apprise)

'retain for matrimonial cases' is the wordplay.
'cases' says the answer is hidden in the clue.
'INFORM' is hidden within 'retain for matrimonial'.

(Other definitions for inform that I've seen before include "Provide facts - playing well" , "Put wise" , "Advise, acquaint with" , "Tell - shop" , "Enlighten" .)

I've seen this clue in The Telegraph.

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