The Collaborative International Dictionary of English v.0.48:
Perfidiousness \Per*fid"i*ous*ness\, n. The quality of being perfidious; perfidy. --Clarendon. [1913 Webster]WordNet (r) 3.0 (2006):
perfidiousness n 1: betrayal of a trust [syn: perfidy, perfidiousness, treachery]