Odes Enid altered - that's unfair (3-5)
I believe the answer is:
one-sided
'unfair' is the definition.
(I've seen this before)
'odes enid altered' is the wordplay.
'altered' indicates an anagram.
'odes'+'enid'='odesenid'
'odesenid' with letters rearranged gives 'ONE-SIDED'.
'that's' acts as a link.
(Other definitions for one-sided that I've seen before include "Indeed so (anag.)" , "Unequal like contest between badly matched opponents" , "Grossly unequal; biased" , "So denied being partisan or unfair" , "Unfair or uneven" .)