Going back again to the same river (4)
I believe the answer is:
oder
'river' is the definition.
(River Oder in central Europe)
'going back again to the same' is the wordplay.
'going back' shows that the letters should be reversed in order.
'again' becomes 're' (prefix meaning 'again').
'to the same' becomes 'do' (abbreviation for ditto).
're'+'do'='redo'
'redo' back-to-front is 'ODER'.
(Other definitions for oder that I've seen before include "river, one in central Europe" , "River forming northern part of the German-Polish border" , "German and Polish river" , "School blazer insignia" , "flowing water" .)