E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
means what is due or owing, a debt which should be paid. Thus obedience is the debt of citizens to rulers for protection, and service is the debt of persons employed for wages received.
Strictly considered, all duty is owed originally to God only; but . . duties to God may be distributed into duties towards self, towards manhood, and towards God.Gregory: Christian Ethics, part ii. division i. p. 172.