积怨 literally means 'accumulated resentment' — the character 积 (jī) means 'to accumulate' or 'to build up over time', while 怨 (yuàn) means 'resentment', 'grudge', or 'bitterness'. Together, 积怨 refers to deep-seated, long-standing ill will that develops gradually, often due to repeated slights, unresolved conflicts, or unaddressed injustices. It implies emotional weight and duration, not a fleeting irritation.

This noun is commonly used in formal or literary contexts — such as discussions of interpersonal relationships, workplace tensions, historical grievances, or social conflicts. It often appears with verbs like 产生 (to arise), 深化 (to deepen), or 化解 (to resolve). Because it conveys seriousness and emotional gravity, 积怨 is rarely used lightly or humorously; it signals a significant, entrenched negative feeling that may require deliberate effort to heal.