What is "epiousios"

Epiousios ( Koine Greek: επιούσιος) is a highly unique Greek word used in the fourth petition of the Lord's Prayer, as recorded in the Gospel of Matthew (Matthew 6:11) and the Gospel of Luke (Luke 11:3). The word epiousios is not found anywhere else in the original scriptures of the Bible, nor anywhere else in all of ancient Greek literature. Epiousei used in Acts 7:26 to refer to the next day may be a related word.

While epiousios is often substituted by the word "daily," all other New Testament translations from the Greek into "daily" otherwise reference hemeran (ἡμέραν, "the day"), which does not appear in this usage.

There are several reasons as to why epiousios presents an exceptional translation challenge. The word appears nowhere else in other Ancient Greek texts, and so may have been coined by the authors of the Gospel. Another challenge is that Jesus would either have spoken his native Aramaic language or Hebrew, and the consensus view is that the language of the New Testament was originally written in a form of Koine Greek. By tradition, the most common English language translation is daily, though most scholars today reject this. The Catholic Church, the largest Christian denomination by far, holds the view in its Catechism that there are several ways of interpreting epiousios, including the traditional daily. Alternative theories are that—aside from the etymology of ousia, meaning substance—it may be either derived from the verb to be or from the word verb ienai, meaning both to come and to go.