The Collaborative International Dictionary of English v.0.48:

Dispassionate \Dis*pas"sion*ate\, a.
   1. Free from passion; not warped, prejudiced, swerved, or
      carried away by passion or feeling; judicial; calm;
      composed.
      [1913 Webster]

            Wise and dispassionate men.           --Clarendon.
      [1913 Webster]

   2. Not dictated by passion; not proceeding from temper or
      bias; impartial; as, dispassionate proceedings; a
      dispassionate view.

   Syn: Calm; cool; composed serene; unimpassioned; temperate;
        moderate; impartial; unruffled. --
        Dis*pas"sion*ate*ly, adv. -- Dis*pas"sion*ate*ness,
        n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

dispassionateness
    n 1: objectivity and detachment; "her manner assumed a
         dispassion and dryness very unlike her usual tone" [syn:
         dispassion, dispassionateness, dryness]