Fair flat (4)
I believe the answer is:
even
I believe this is a double definition.
'fair' is the first definition.
(I've seen this before)
'flat' is the second definition.
(similar in meaning)
(Other definitions for even that I've seen before include "draw" , "Not odd; flat" , "When darkness starts to fall" , "Still - flat" , "time when sun goes down for the poet" .)