Epiousios is one of the most debated words in the entire NT — it appears only twice (Matthew 6:11 and Luke 11:3) in the Lord's Prayer: 'Give us this day our epiousios bread.' The word does not appear in any other Greek literature before the NT, making its meaning uncertain. Scholarly interpretations: (1) 'daily' bread, what is needed for today; (2) 'bread for the coming day' (tomorrow's provision asked today); (3) 'super-substantial' bread (Jerome's Vulgate) — pointing to the Eucharist; (4) 'necessary for existence' — essential bread.
Regardless of precise etymology, the theology is clear: we are to ask God for provision one day at a time, trusting His daily care. This is the manna theology — God provided enough for each day, not a year's supply. Asking for epiousios bread keeps us in daily dependence on the Father. The 'bread' may also be the living Bread of John 6 — Christ Himself as our daily sustenance. Either way, this unique NT word anchors the Christian life in moment-by-moment dependence on God.