One-sided United Nations trade exhibition (6)
I believe the answer is:
'one-sided' is the definition.
(similar in meaning)
'united nations trade exhibition' is the wordplay.
'united nations' becomes 'UN' (abbreviation).
'trade exhibition' becomes 'fair' (fair is a kind of exhibition. I am not sure about the 'trade' bit.).
Can you help me to learn more?
(Other definitions for unfair that I've seen before include "Swizz!" , "Not equitable or blond" , "Not just - lacking in beauty" , "out of order" , "Not equitable - or blonde?" .)