betrayal
n.an act of hurting someone who trusts you, such as a friend or partner. It happens when you break a promise or help an enemy.
n.the act of violating trust, confidence, or an inherited bond of loyalty. Often involves aiding an adversary or failing to uphold a moral or personal commitment.
“Sharing her secret with the whole school was a huge betrayal.”
“He felt a deep sense of betrayal when he discovered his business partner had been stealing from the company.”
“The novel explores the psychological impact of political betrayal, focusing on how a single informant's actions destroyed an entire underground resistance movement.”
Uncountable when referring to the abstract concept of disloyalty; countable when referring to specific instances or acts.
“Outlining why Patterson's crime was so "dreadful", they talked of the "betrayal of trust" of family members whom she had invited for lunch.”
From betray + -al.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.