English word “piety” comes from Latin noun pietas. Regarding pietas, Cicero (De Inuentione. II, 65-66) says that
[…] some things seem to be a law of nature, which brings to us not an opinion, but a certain innate force, as religion, piety [pietas], gratitude, avenging, obedient observance, and truth. […] they call piety [pietas] what warns us to keep our duty towards our motherland, our parents or others connected with us by blood […].
Pietas, a Latin concept in itself, is used to translate the Ancient Greek term εὐσέβεια (which is also personified in the daimona Eusebeia). Considering the term, W. Buckert says:
Yet the act of sebesthai [to worship] itself does not constitute meritorious piety, it only becomes such when it is subjected to the criterion of the good; this is eusebeia. The sole criterion available is the custom of the ancestors and of the city, nomos: ‘to change nothing of what our forefathers have left behind’, this is eusebeia.
The following excerpt from Isocrates (7. 30) helps to illustrate the concept:
For their only care was not to destroy any institution of their fathers and to introduce nothing which was not approved by custom, believing that reverence [εὐσέβεια] consists, not in extravagant expenditures, but in disturbing none of the rites which their ancestors had handed on to them.
So, put simply, being pious, in its true meaning, which is a Pagan one, is to fulfill your duties to your land and your ancestors, their gods and customs – which are, by extension, your own gods and customs.
That both pietas and εὐσέβεια were used to translate the Hebrew concept of “fear of the god” (וְיִרְאַת יְהוָה) and that this meaning (alongside other derivative senses coming from Christian thought, such as the idea of approaching the dreadful god with humility, trust and love) was the one to enter our modern languages, that is disgraceful. Yet this word’s true, Pagan, meaning is still available, and from this meaning we must take the image of pious men and women we all must be: those who have reverence for our lands, our ancestors, our gods, our heritage.