It's simply not fair (4)
I believe the answer is:
ugly
'not fair' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for ugly that I've seen before include "Unpleasing to the eye" , "not tasty?" , "Far from beautiful" , "Extremely unattractive" , "Grotesque" .)