Short-lived Conservative after terrible strain (10)
I believe the answer is:
transitory
'short-lived' is the definition.
('transitory' can be a synonym of 'short-lived')
'conservative after terrible strain' is the wordplay.
'conservative' becomes 'tory' (I've seen this before).
'after' is a charade indicator (letters next to each other).
'terrible' indicates an anagram.
'strain' with letters rearranged gives 'transi'.
'tory' after 'transi' is 'TRANSITORY'.
(Other definitions for transitory that I've seen before include "Here-today-gone-tomorrow" , "Ephemeral" , "Short-lived" , "Fleeting" , "Brief" .)