Die down (5)
'die down' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for abate that I've seen before include "Become less intense" , "Let up or die away" , "Moderate" , "Put an end to" , "(Flood) recede" .)
'die down' is the definition.
(subsiding is a kind of diing down)
This is the entire clue.
(Other definitions for subside that I've seen before include "Wane" , "Abate" , "(Of floods) go down" , "Fall back" , "Collapse" .)