Prefix with aggression
I believe the answer is:
micro
'prefix with aggression' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for micro that I've seen before include "Prefix meaning very small or one millionth" , "Prefix meaning tiny, or one-millionth of a unit" , "needed in kitchen-sink dramas?" , "Very little" , "Extremely small" .)