Judge to decide a disputed issue (7)
I believe the answer is:
arbiter
'judge to decide a disputed issue' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for arbiter that I've seen before include "Rarebit? (anag)" , "Decision maker" , "Rear bit (anag.)" , "Settler of dispute" , "One has the authority to settle disputes" .)