Smear, brutal, unfair - extremely (4)
I believe the answer is:
blur
'smear' is the definition.
(synonyms)
'brutal unfair extremely' is the wordplay.
'brutal' becomes 'bl' (I can't explain this - if you can you should believe this answer much more).
'extremely' suggests removing the centre (only the extremes of the word are used).
'unfair' with its middle removed is 'ur'.
'bl'+'ur'='BLUR'
Can you help me to learn more?
(Other definitions for blur that I've seen before include "Out-of-focus sight" , "Become unclear" , "Make or become indistinct" , "Fuzzy image" , "Indistinct representation - obscure" .)