The Complicated Uses of Pious

Pious has a bit of an image problem. From the beginning of its use in the 15th century this Latin descendant has been used to describe those who are simply very religious—that is, who are deeply devoted to their religion—but it has for centuries also described those who make a show of their religiousness and use it to assert their superiority. We see both in literature:

She sent for a minister, too, a serious, pious, good man, and applied herself with such earnestness, by his assistance, to the work of a sincere repentance, that I believe, and so did the minister too, that she was a true penitent….
— Daniel Defoe, Moll Flanders, 1722

There are a thousand hacking at the branches of evil to one who is striking at the root, and it may be that he who bestows the largest amount of time and money on the needy is doing the most by his mode of life to produce that misery which he strives in vain to relieve. It is the pious slave-breeder devoting the proceeds of every tenth slave to buy a Sunday's liberty for the rest.
— Henry David Thoreau, Walden, 1854

Over the years other meanings have developed too. Pious can be used positively to describe those who are dutiful or virtuous, or things that are worthy. And it can be used negatively to describe hypocrisy. It is also used neutrally to distinguish what is religious from what is nonreligious in content, as in this humorous excerpt from Emily Brontë's 1847 Wuthering Heights:

Joseph was an elderly, nay, an old man—very old, perhaps, though hale and sinewy. "The Lord help us!" he soliloquized in an undertone of peevish displeasure, while relieving me of my horse, looking, meantime, in my face so sourly that I charitably conjectured he must have need of divine aid to digest his dinner, and his pious ejaculation had no reference to my unexpected advent.

Because the word is about religion and religiousness, many associate pious with the Bible. It is, however, wholly absent from many translations of the Bible, probably because of its ambiguous meaning. Pious is, though, included in The New Revised Standard Version and the paraphrasing Living Bible, among a number of others:

The blessing of the Lord is the reward of the pious, and quickly God causes his blessing to flourish.
— Sirach 11:22, New Revised Standard Version

You try to look like saintly men, but underneath those pious robes of yours are hearts besmirched with every sort of hypocrisy and sin.
— Matthew 23:28, The Living Bible

Piety, which most often refers to simple religious devotion, doesn't have the same problem, and is more widely used in biblical translations.