The Collaborative International Dictionary of English v.0.48:

Unbiased \Un*bi"ased\ ([u^]n*b[imac]"ast), a. [Pref. un- not +
   biased.]
   Free from bias or prejudice; unprejudiced; impartial. --
   Un*bi"ased*ly, adv. --Un*bi"ased*ness, n.
   [1913 Webster] Unbid