The Collaborative International Dictionary of English v.0.48:

Disdainful \Dis*dain"ful\, a.
   Full of disdain; expressing disdain; scornful; contemptuous;
   haughty.
   [1913 Webster]

         From these
         Turning disdainful to an equal good.     --Akenside.
   -- Dis*dain"ful*ly, adv. -- Dis*dain"ful*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

disdainfulness
    n 1: the trait of displaying arrogance by patronizing those
         considered inferior [syn: condescension,
         superciliousness, disdainfulness]