Serbia sedulously protecting partisan (6)
I believe the answer is:
biased
'partisan' is the definition.
('biased' can be similar in meaning to 'partisan')
'serbia sedulously protecting' is the wordplay.
'protecting' indicates a hidden word.
'BIASED' is hidden in the letters of 'serbia sedulously'.
(Other definitions for biased that I've seen before include "Having favourite" , "Influenced unfairly" , "Not impartial" , "'One-sided, slanted (6)'" , "Prejudiced or influenced in favour or against" .)