...with left suffering decline (8)
I believe the answer is:
languish
'decline' is the definition.
(I've seen this before)
'with left suffering' is the wordplay.
'with' means one lot of letters go next to another.
'left' becomes 'l' (common abbreviation).
'suffering' becomes 'anguish' (anguish is a kind of suffering**).
'l' next to 'anguish' is 'LANGUISH'.
(Other definitions for languish that I've seen before include "Grow weak or feeble" , "Suffer neglect" , "Lose or lack vitality" , "go into decline" , "Long" .)