To harbor resentment or hold a grudge in one's heart.
把怨恨藏在心里。形容对人记下仇恨，以伺机报复。
明·冯梦龙《警世通言》第二十四回知县听玉姐说了一会，叫‘皮氏，想你见那男子弃旧迎新，你怀恨在心，药死亲夫，此情理或有之。’”
She felt betrayed and held a grudge against him for years.
Learn the next connected idiom: 怀恨在心 (huái hèn zài xīn) → 心有余悸 (xīn yǒu yú jì)
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