He's not treated in a fair way (6)
I believe the answer is:
honest
'fair way' is the definition.
'honest' can be an answer for 'fair' (I've seen this before). I'm unsure of the 'way' bit.
'he's not treated' is the wordplay.
'treated' indicates an anagram.
'hes'+'not'='hesnot'
'hesnot' is an anagram of 'HONEST'.
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for honest that I've seen before include "Frank" , "Not disposed to cheat" , "Truthful and trustworthy" , "Law-abiding" , "Direct" .)