Combining 怨 (grievance) and 恨 (hatred) creates a powerful compound word. It describes a feeling that starts with a specific grievance (怨) and then hardens into a deep, lasting hatred (恨).
In Chinese culture, where harmony (和谐, héxié) and interpersonal relationships (关系, guānxi) are highly valued, 怨恨 (yuànhèn) is a particularly heavy and disruptive emotion. It often arises from a violation of core values like fairness (公平, gōngpíng) or loyalty (忠诚, zhōngchéng). A useful Western comparison is “holding a grudge,” but 怨恨 often feels deeper and more profound. While Western psychology often emphasizes “letting go” for one's own mental health, in Chinese literature and historical narratives, harboring 怨恨 can sometimes be portrayed as a righteous, albeit painful, response to a grave injustice that has caused a loss of “face” (面子, miànzi) or brought shame to a family. It's an emotion that can fuel epic tales of revenge and quests for justice that span generations, a common theme in Wuxia (武侠) novels and historical dramas.
怨恨 is a strong and serious word. You would not use it for minor annoyances. Its usage implies a deep emotional wound.