Transient (9)
There are a few possibilities for this:
ephemeral
'transient' is the definition.
(I know that transient can be written as ephemeral)
This is all the clue.
(Other definitions for ephemeral that I've seen before include "Fugitive" , "Having only brief existence" , "A mere help (anag) - short-lived" , "Transient, fleeting" , "Short-lived, passing quickly" .)
'transient' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for temporal that I've seen before include "Secular; of the temples" , "on the Head's side?" , "about the side of the head" , "Worldly, secular" , "profane" .)
(Other definitions for fleeting that I've seen before include "Lasting for a brief time" , "Transient" , "Momentary" , "Evanescent" , "Ephemeral" .)