duty: [13] Duty comes from Anglo-Norman dueté. This was a derivative of Old French deu ‘owed’ (source of English due [13]), which in turn came from Latin dēbitus, past participle of dēbēre ‘owe’ and source of English debit and debt. (Latin dēbēre was originally a compound verb formed from the prefix dē- ‘away’ and habēre ‘have’, literally ‘have away’, that is ‘keep in one’s possession what belongs to someone else’.) So etymologically one’s duty is what one ‘owes’ to others. => debit, debt, due[duty etymology, duty origin, 英语词源]