expression, godan verb (-ru, irregular)
to be in someone's debt; to owe someone a favor
Expresses a sense of gratitude and obligation toward someone who has done a kindness. Often used in formal or heartfelt contexts.
彼には大変恩がある。
I am deeply indebted to him.
あなたに恩があることは忘れません。
I will not forget that I owe you a debt of gratitude.
Similar meaning but more colloquial and often used when directly thanking someone. 恩がある is more about the state of being indebted.
Literally 'to have a debt', can be used for both financial and moral debts, but 恩がある specifically refers to a moral debt of gratitude.
Compound of 恩 (おん, 'favor, kindness') + が (subject marker) + ある ('to exist, to have'). The expression literally means 'there is a kindness' and idiomatically means 'to be indebted'.