English

Noun

treacherousness ‎(uncountable)

1. Treachery; the characteristic of being treacherous.
   • 1901, Bret Harte, "Under the Eaves", in Under the Redwoods,

     He had an aggressive treacherousness of eye which his potations had not subdued.

References

• “treacherousness” in An American Dictionary of the English Language, by Noah Webster, 1828.
• “treacherousness” in Dictionary.com Unabridged, v1.0.1, Lexico Publishing Group, 2006.