Spirit ultimately haunting wide Russian river (6)
I believe the answer is:
geneva
'spirit ultimately' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'haunting wide russian river' is the wordplay.
'haunting wide' becomes 'ge' (I can't explain this - if you can you should believe this answer much more).
'russian river' becomes 'neva' (I've seen this in another clue).
'ge'+'neva'='GENEVA'
Can you help me to learn more?
(Other definitions for geneva that I've seen before include "Alpine lake" , "City and lake in SW Switzerland" , "International agreement on the treatment of civilians and captured or wounded military personnel in wartime" , "Swiss city, lake" , "old Calvinist stronghold" .)