Relent, a dispute is endless (7)
I believe the answer is:
eternal
'endless' is the definition.
(I know that endless can be written as eternal)
'relent a dispute' is the wordplay.
'dispute' is an anagram indicator (I've seen 'disputed' mean this).
'relent'+'a'='relenta'
'relenta' is an anagram of 'ETERNAL'.
'is' acts as a link.
(Other definitions for eternal that I've seen before include "Lasting forever, tediously persistent" , "Existing forever" , "Never-ending, existing always" , "what should be unchangeable" , "Everlasting, not affected by time" .)