IMPARTIAL=DISINTERESTED=NEUTRAL=UNBIASED >< PARTIAL=INTERESTED=BIASED

(adjective) unbiased, disinterested, favouring neither party.
"The dispute will be resolved through the offices of an impartial third party."
Synonyms:
-------disinterested: "The parties chose a disinterested attorney to mediate their dispute."
-------neutral: "The court ordered a neutral observer to oversee the psychological examination of the defendant."
Antonyms:
-------biased: "All advocacy is, by definition, biased advocacy."
-------partial: "The presence of a partial juror, who had not disclosed that she held stock in the plaintiff company, resulted in a new trial of the case."
Other forms of the word:
-------impartiality: "Nobody questioned the judge's impartiality."
Common phrases: impartial third party / impartial observer / impartial arbitrator / impartial judge
Common mistake: While "partial" can also mean "not whole", impartial does not mean whole. The opposite of partial in that usage is "complete".
Related concepts:
-------OBJECTIVE: not influenced by personal feelings "A good judge takes an objective approach to every case."
Source: Translegal