Die down, diminish (5)
I believe the answer is:
abate
I believe this is a double definition.
'die down' is the first definition.
(I've seen this in another clue)
'diminish' is the second definition.
(abating is a kind of diminishing)
(Other definitions for abate that I've seen before include "Diminish, mitigate" , "(Flood) recede" , "Let up or die away" , "Become less strong like storm" , "Go down like storm" .)