The Collaborative International Dictionary of English v.0.48:

Impartial \Im*par"tial\, a. [Pref. im- not + partial: cf. F.
   impartial.]
   Not partial; not favoring one more than another; treating all
   alike; unprejudiced; unbiased; disinterested; equitable;
   fair; just. --Shak.
   [1913 Webster]

         Jove is impartial, and to both the same. --Dryden.
   [1913 Webster]

         A comprehensive and impartial view.      --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

impartial
    adj 1: showing lack of favoritism; "the cold neutrality of an
           impartial judge" [ant: partial]
    2: free from undue bias or preconceived opinions; "an
       unprejudiced appraisal of the pros and cons"; "the impartial
       eye of a scientist" [syn: unprejudiced, impartial] [ant:
       discriminatory, prejudiced]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "impartial":
   Laodicean, Olympian, apathetic, candid, centrist, detached,
   disinterested, dispassionate, equal, equitable, even, evenhanded,
   fair, fifty-fifty, half-and-half, impersonal, independent,
   indifferent, just, lofty, midway, moderate, neuter, neutral,
   nonaligned, noncommitted, nonpartisan, objective, on the fence,
   passive, selfless, third-force, third-world, unbiased, uncolored,
   uncommitted, undazzled, uninfluenced, uninvolved, unjaundiced,
   unprejudiced, unprepossessed, unselfish, unswayed



The Devil's Dictionary (1881-1906):

IMPARTIAL, adj.  Unable to perceive any promise of personal advantage
from espousing either side of a controversy or adopting either of two
conflicting opinions.