Evil, snaffling weapon - one from both sides? (8)
I believe the answer is:
balanced
'one from both sides?' is the definition.
(as in a balanced debate)
'evil snaffling weapon' is the wordplay.
'evil' becomes 'bad' (similar in meaning).
'snaffling' means one lot of letters goes inside another (snaffle can mean to take or steal).
'weapon' becomes 'lance' (lance is a kind of weapon).
'bad' placed around 'lance' is 'BALANCED'.
(Other definitions for balanced that I've seen before include "With both sides equal" , "Auntie is supposedly" , "In a state of equilibrium" , "Equipoised" , "Having different elements in the correct proportions, in a diet say" .)