Belligerent cook varies eggs (10)
I believe the answer is:
aggressive
'belligerent' is the definition.
(synonyms)
'cook varies eggs' is the wordplay.
'cook' indicates anagramming the letters.
'varies'+'eggs'='varieseggs'
'varieseggs' anagrammed gives 'AGGRESSIVE'.
(Other definitions for aggressive that I've seen before include "Belligerent" , "Showing anger" , "Rudely hostile" , "Forceful" , "Vigorous" .)