Hi Manfred,
Here’s the Greek again, we’ll start with Luke which is clearer.
??? is the word in question.
Luke 11:3
τ-ον αρτ-ον ημων τ-ον επιουσι-ον
the/As bread/As of-us/Gp the/As ???/As
διδου ημιν το καθ ημερ-αν
give!/2sImp! to-us/Dp the/N/As according-to day/As
Luke already has an expression for daily – eg:according to day.
“Give us, according-to day, the bread of us * the ??? bread.”
The structure indicates there is more than one kind of “our bread/bread of us” which can be given daily, and a specific one qualified by ??? is intended.
Matth 6:11 τ-ον αρτ-ον ημων τ-ον επιουσι-ον δος ημιν σημερ-ον
Matth 6:11 the/As bread/As of-us/Gp the/As ???/As give/2sImp! to-us/Dp today/As
“Give to-us today, the bread of-us * the ??? bread”
If the word were truly a derivative of subsist, there ought to be some clear examples outside the bible – or perhaps I can look up a derivation and check the steps – so far nothing promising. It is true that επι could be formed by contractions from other words – as that is the problem with that particular prefix.
But, the very fact that the word is nearly unique, suggests that it is not a kind of bread people would normally have. Also, Since Luke and Matthew use the same phrase – epi-ousi-on ( επι-ουσι-ον) – there is a very good chance the word was coined for a reason specific to Jesus since Luke’s is writing for a different Greek audience than Matthew (the more Hebrew of the two). There is no poetic sound to explain the reason for redundancy in Luke’s version – Giving bread daily, gets the message across – rather than Matthew’s ‘today’ – so Luke had no reason to repeat it, except to mark the bread as special in some way.
There are examples of εκ-ουσι-ον, and περι-ουσι-ον, which means that if the word isn’t substance/wealth/material ουσι-α (because of a different gender), but is a distinct word ουσι-ον, or one formed by contraction – then it must have the same meaning as the other examples ending in ουσι-ον.
It looks very likely that the word could mean founded/upon/above(επι) - wealth/material/substance( ουσι-ον ).
A bread upon [another?] substance.
Also note the pun, “our bread” or “bread of us” – can mean we are the bread (the body of christ) which fits scripturally too.**