English

Noun

perfidiousness ‎(usually uncountable, plural perfidiousnesses)

1. (rare) Unfaithfulness; deceitfulness; perfidy.
   • 1781, Samuel Johnson, "Addison" in Lives of the Poets:

     Not only Cato is vanquished by Caesar, but the treachery and perfidiousness of Syphax prevail over the honest simplicity and the credulity of Juba.

Related terms

• perfidious
• perfidiously

References

• “perfidiousness” in An American Dictionary of the English Language, by Noah Webster, 1828.
• perfidiousness in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913
• “perfidiousness” in Dictionary.com Unabridged, v1.0.1, Lexico Publishing Group, 2006.