The Collaborative International Dictionary of English v.0.48:

Imperiousness \Im*pe"ri*ous*ness\, n.
   The quality or state of being imperious; arrogance;
   haughtiness.
   [1913 Webster]

         Imperiousness and severity is but an ill way of
         treating men who have reason of their own to guide
         them.                                    --Locke.
   [1913 Webster]

WordNet (r) 3.0 (2006):

imperiousness
    n 1: the trait of being imperious and overbearing [syn:
         imperiousness, domineeringness, overbearingness]