Noun
debt of honor (plural debts of honor)
(US, set phrase) An obligation, especially a gambling debt based on a verbal promise, which is not legally enforceable but which is considered to be secured by the debtor's moral integrity.
So John, fulfilling a debt of honor, sets out to teach Alex how to protect himself. Source: Internet
When it becomes clear that local law enforcement has direct connections to the murder itself, John realizes that to repay his debt of honor, he must teach Alex Martin how to protect himself, even if that means teaching Alex to kill. Source: Internet