treachery
noun /ˈtretʃəri/
  /ˈtretʃəri/
[uncountable, countable] (plural treacheries)
- behaviour that involves hurting somebody who trusts you, for example by telling their secrets to other people; an example of this
- an act of treachery
 - He was punished for his treacheries.
 - Rumours of treachery and conspiracy began to circulate in the Queen’s court.
 
Word OriginMiddle English: from Old French trecherie, from trechier ‘to cheat’.