The word ἐπιούσιον has been translated in numerous ways, but the greatest modern consensus is to translate the word as 'daily.' Was the word ἐπιούσιον used prior to the Lord's prayer (Matthew 6:11; Luke 11:3)? What does it mean?
Bruce M. Metzger writes in Bibliotheca Sacra 150 (July-September 1993) (pp 277–278):
Context might give us some clues. It sounds a bit odd to ask for tomorrow's bread today (σήμερον). Also, given Jesus' subsequent instructions to not be anxious about what we will eat, drink, and wear, the context lends itself to "daily" or regular bread. Especially striking is:
So Jesus seems to teach that we ought to pray for our needs and then trust God to deliver.
Wikipedia cites A Greek-English Lexicon of the New Testament and Other Early Christian Literature for the primary definition of the word:
It should be noted that Jerome only used supersubstantialem for Matthew's version of the prayer.
Chrysostom seems to take the word mean both daily and needful:
Origen considers "needful" to be a better translation than "daily":
We can make an educated guess about what Matthew, Luke, or their common Greek source (Q) meant by ἐπιούσιον from context, etymology, and historical translations. The various proposals ("needful", "daily", and "for tomorrow") cluster around the idea that we should ask for the required sustenance that ultimately only God can give.
What does this word mean and connotate?
When the Israelites were in the wilderness, the manna appeared as an act of God's command, and so they were not mediately dependent on the manna for survival as much as they were immediately dependent upon God's very commandment, which brought the manna into existence in the first place. (Jesus quoted this line of reasoning to the devil by citing Deut 8:3 in this exact context.) The subsistence of bread therefore has to do with our reliance or dependence on the words of God, which for the Israelites was a "daily" occurance in the wilderness.
Now if our "inheritance" in the New Testament is not the geographical area of Palestine, but the heavenly Jerusalem above (Gal 4:26 and Heb 12:22), then our sojourn on the earth is indeed a wilderness journey of trials and temptations. Until we "cross the Jordan," we are "daily" in need of the words of God. These words not only provide the grace to give us "daily" food as nourishment for our bodies (for which we are of course grateful), but are also the very words that bestow eternal life upon us.
It is interesting that Jesus described himself as the manna from heaven (John 6:51), and then Peter replied that it was that Jesus had the very words of eternal life (John 6:68). So the words, or commandments of God, are the very source of life. It is no surprise then that Jesus is also personified as the "Word of God" in the New Testament.
In Exodus 16:4, the narrative indicates that the Lord had served "le mot du jour" to the Israelites as their food.
Ex 16:4 (NASB)
In Biblical Hebrew, there is a play on words here (which I have highlighted in bold above). That is, the phrase "דְּבַר־יֹום" is not an adverbial phrase of time (as can be found in the Hebrew text of Ex 5:13 or Ex 5:19, for example), but is an objective phrase in Hebrew. That is, this phrase is the object of the Hebrew verb לָקַט, to gather or pick up. (In Ex 5:13 or Ex 5:19, "mud bricks" function as the object of the transitive verb לָקַט, and in those verses דְּבַר־יֹום functions as an adverbial phrase of time.) But in Ex 16:4 we read that the Israelites gathered "le mot du jour" from heaven in order to eat it -- that is, they were eating the DAILY ALLOTMENT of the WORD (of God). We know that this juxtaposition of meaning is certain because Deut 8:3 says so.
So the manna from heaven was the Daily Word ("Mot du Jour") from heaven. God's word therefore was their DAILY food.
Take the word apart: έπι + ούσιον = on/upon/above essence/substance. It most likely means "necessary for existence" or "more than necessary." Origen taught that the Evangelists invented the word. The earliest translations into Syriac interpreted the word as continual or for our need. Supersubstantialis was the original translation into Latin by Jerome, but it was later changed to quotidianus, meaning "daily," in Velus Itala. English is based on the rendering from Latin. But the Orthodox Greeks, Slavs and Russians kept the original sense of the unique word when they recite the Lord's Prayer.
Origen, Chrysostom, and Jerome all understood it as "necessary for existence." This early Christian understanding (which is still retained by the Eastern Orthodox Church) has nothing to do with daily needs such as bread we eat for calories in our diet. Why would Jesus turn around and tell his disciples not to worry about food and drink right after telling them to ask God for it? The Latin best transliterates into English: this is "supersubstantial" bread that we pray for. It is a play on words also (deriving from ἐπιέναι/ἐπιόν): it is the bread of the age to come. Jesus himself is the bread of life; his bread is spiritual bread of eternal life. The Eastern Orthodox Church believes that it partakes of this bread in the Mystical Supper every Sunday.
Most evangelicals assert that it simply means "daily" and thus avoid the sacramental and eschatological language concerning the 'nature/essence' of the bread. Eastern Orthodox Christians believe that this rejection of the sacraments and this sort of language in scripture represents a quasi-Gnostic worldview. That is, the early Christians viewed the world only in terms of Uncreated (God) versus created (everything/one else). The Gnostics viewed the world as a dualism between physical matter and the spiritual realm, a worldview which early Christians rejected. Modern (post-Enlightenment) evangelicals often share this Gnostic dualistic worldview which rejects that physical and spiritual elements can both be holy and even mystically conjoined.
We have no records of the word being used prior to the Lord's prayer. The NET Bible translates:
They then note that other potentially valid translations would include “Give us bread today for the coming day,” or “Give us today the bread we need for today.”
Unfortunately, the Greek term appears only in early Christian literature such as Luke 11:3 and the Didache 8:2. Therefore, we have little to work with.
Working from the construction of the word and possible related words, we find επιουσιος might be related to επιουσα which means "tomorrow."