Savage fellow left after a long time (5)
I believe the answer is:
feral
'savage' is the definition.
(I know that savage can be written as feral)
'fellow left after a long time' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'left' becomes 'l' (common abbreviation).
'after' means one lot of letters go next to another.
'a long time' becomes 'era' (a long period of time).
'l' after 'era' is 'eral'.
'f'+'eral'='FERAL'
(Other definitions for feral that I've seen before include "Wild but originally domestic" , "Wild and menacing" , "Flare up, being fierce" , "Flare up in wild state" , "Flare up, going wild" .)