Country's source of Russian river (5)
I believe the answer is:
rural
'country's' is the definition.
('rural' can be similar in meaning to 'country')
'source of russian river' is the wordplay.
'source of' indicates taking the first letters.
'river' becomes 'ural' (I've seen this before**).
The first letter of 'russian' is 'r'.
'r'+'ural'='RURAL'
(Other definitions for rural that I've seen before include "Countrified" , "Countrylike" , "Connected with farming" , "Arcadian" , "Sort of dean" .)