Just after turning back, first arrive at hell (7)
I believe the answer is:
inferno
'hell' is the definition.
('inferno' can be a synonym of 'hell')
'just after turning back first arrive at' is the wordplay.
'just after' becomes 'on'.
'turning back' says the letters should be written backwards.
'first' means one lot of letters go next to another.
'arrive at' becomes 'infer' (inferring is a kind of arriving at).
'on' in reverse letter order is 'no'.
'no' put after 'infer' is 'INFERNO'.
(Other definitions for inferno that I've seen before include "Uncontrollable fire" , "Intense and uncontrolled fire" , "Hellish poem" , "Large and out-of-control fire" , "Huge conflagration" .)