debt of honor; debt of honour
A debt that is not legally enforceable but is considered binding by social or moral obligation; often used in contexts of personal trust or reputation.
He worked desperately to repay his debt of honor.
A debt of honor is not a legal debt, but it must be repaid out of moral duty.
Compound of 信用 (trust, credit) and 借り (debt, borrowing). The exact historical derivation is uncertain, but the term likely emerged to describe obligations based on personal trust rather than legal contracts.