Treachery is the betrayal of somebody who trusted you. The wound is the trust, not the act.
It is a heavier word than betrayal and belongs to war, politics and epic stories, where an act of treachery changes everything. The trust is essential, since a stranger cannot commit treachery against you. The adjective treacherous has a second and very common physical sense meaning dangerously unreliable, so treacherous ice and a treacherous bend are hazards rather than traitors. Treason is the specific crime of betraying your country.
1nountreacheryBetrayal of trust.
“He never forgave what he saw as treachery.”
Treachery is cheating. Old French tricher meant to cheat, so the word began as a swindle and only afterwards took on the weight of betrayal.
Old French
tricherie
Middle English
trecherie
English, today
treachery
Built from
From Middle English trecherie, from Old French tricherie, trecherie, from tricher, trichier (“to cheat”).
Etymology from Wiktionary, CC BY-SA