Short-lasting (9)
I believe the answer is:
ephemeral
'short-lasting' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ephemeral that I've seen before include "just for a day?" , "Transient, fleeting" , "short term gain" , "Having only brief existence" , "A mere help (anag) - short-lived" .)