Death occurring within seven days (3)
I believe the answer is:
end
'death' is the definition.
(synonyms)
'occurring within seven days' is the wordplay.
'occurring within' says the answer is hidden in the clue.
'END' is hidden within 'seven days'.
(Other definitions for end that I've seen before include "SECOND PART OF 24" , "Conclusion of agenda" , "death" , "Aim; stop" , "Fine" .)