Here’s a quote from Russell McCutcheon et al.’s terrific website Studying Religion:
As already noted, in Ancient Greek, the term eusebia, or in Latin pietas, signified reverence, honor, and esteem–notably as expressed in social and legal relationships. Examples would include the “proper” relations between husband and wife, parent and child, master and slave, soldiers and commanders, and as well, between mortals and the immortals. For example, a “pious” Greek would engage in the proper rituals with regard to various gods but would also ensure that relations with superiors, peers, and inferiors were carried out according to the rules of propriety. In Plato’s ancient Greek society, eusebia therefore signified the system of conventional and ordinary social practices concerning one’s relations with others–relations that extend from the family to the gods, from social inferiors to superiors.
This seems like essential background to the exegesis of the New Testament household codes (e.g., Ephesians 5:21-6:9; Colossians 3:18-4:1; 1 Timothy 5:1-16; 1 Peter 2:13-3:9).