Epiousion (ἐπιούσιον) is a Koine Greek adjective used in the Lord's Prayer verse "Τὸν ἄρτον ἡμῶν τὸν ἐπιούσιον δὸς ἡμῖν σήμερον" ('Give us today our epiousion bread'). Because the word is used nowhere else, its meaning is enigmatic - much more significant than the prosaic term "daily".
It is traditionally translated as "daily", but most modern scholars reject that interpretation. The word is also referred to by epiousios, its presumed lemma form.
Since it is a Koine Greek dis legomenon (a word that occurs only twice within a given context) found only in the New Testament passages Matthew 6:11 and Luke 11:3, its interpretation relies upon morphological analysis and context. The traditional and most common English translation is daily, although most scholars today reject this in part because all other New Testament passages with the translation "daily" include the word hemera (ἡμέρᾱ, 'day').
"Daily" (epiousios) occurs nowhere else in the New Testament.
Taken literally (epi-ousios: "super-essential"), this unique word appears to refer directly to the Bread of Life, the Body of Christ, the "medicine of immortality," without which we have no life within us.