Both Uses

treachery
in
King Lear
(Auto-generated)

We have seen the best of our time: machinations, hollowness, treachery, and all ruinous disorders follow us disquietly to our graves.†
Scene 1.2 *

treachery = betrayal
I told him of the army that was landed; He smil'd at it: I told him you were coming; His answer was, 'The worse': Of Gloster's treachery And of the loyal service of his son When I inform'd him, then he call'd me sot And told me I had turn'd the wrong side out:—What most he should dislike seems pleasant to him; What like, offensive.†
Scene 4.2

Definitions:

(1) (treachery)
the behavior of someone who pretends to be a friend and then tricks, cheats, or betrays
(2) (meaning too rare to warrant focus)