adjective (a)

• showing lack of favoritism(adj.all)

  Example:
  The cold neutrality of an impartial judge.
  

  Antonym:
  partial
  

  source: wordnet30
• free from undue bias or preconceived opinions(adj.all)

  Example:
  The impartial eye of a scientist.
  

  Synonym:
  unprejudiced
  Antonym:
  discriminatory, prejudiced
  

  source: wordnet30
• Not partial; not favoring one more than another; treating all alike; unprejudiced; unbiased; disinterested; equitable; fair; just.(adjective)

  source: webster1913