n. Treachery; the characteristic of being treacherous.
The Century Dictionary and Cyclopedia
n. The character of being treacherous: breach of faith or allegiance; faithlessness; perfidy.
Word Usage
"This cannot fail to surprize the Litterary World: who are well acquainted with the treacherousness of memory, and how soon the most happy ideas, for want of sufficient quickness in noting down, are lost in the rapidity of thought."