Extremely warlike and wicked pest (6)
I believe the answer is:
weevil
'pest' is the definition.
(I've seen this before)
'extremely warlike and wicked' is the wordplay.
'extremely' means to remove the middle letters.
'and' is a charade indicator (letters next to each other).
'wicked' becomes 'evil' (synonyms).
'warlike' with its centre removed is 'we'.
'we'+'evil'='WEEVIL'
(Other definitions for weevil that I've seen before include "Small beetle, pest of crops" , "Small kind of 15 down" , "Insect that feeds on plant products" , "Evil we find strangely in a beetle" , "Small beetle, crop pest" .)