Fed up about bride forgetting day, ask for details of service? (7)
I believe the answer is:
debrief
'ask for details of service?' is the definition.
(eg debriefing a member of a secret service)
'fed up about bride forgetting day' is the wordplay.
'fed up' becomes 'def' ('fed' going up in a down clue).
'about' means one lot of letters goes inside another.
'forgetting' is a deletion indicator.
'day' becomes 'd'.
'bride' with 'd' removed is 'brie'.
'def' enclosing 'brie' is 'DEBRIEF'.
(Other definitions for debrief that I've seen before include "Get information from (a returning soldier)" , "Interview after mission (to gather information)" , "Be fired (anag.)" , "Question (returning spy)" , "get the full story" .)