Source of Russian river in the country (5)
I believe the answer is:
rural
'in the country' is the definition.
(I've seen this before)
'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 "Sort of dean" , "Characteristic of country life" , "Relating to the countryside" , "Rustic" , "Bucolic; pastoral" .)