Lasting a very short time (9)
I believe the answer is:
ephemeral
'lasting a very short time' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ephemeral that I've seen before include "not going to last long" , "Fleeting, lasting only a short time" , "Transient, fleeting" , "Transitory" , "Fugitive" .)