Epiousios (ἐπιούσιος) is found only in Matthew 6:11 and Luke 11:3. The fact that it is found nowhere else in the Koine Greek literature that we have makes it seem reasonable to assume that this word was invented by the authors to describe a complex Aramaic word or phrase that Jesus spoke. If that is the case, why did the authors not follow in the style of Matthew 27:46 and include the original Aramaic word or phrase? Has there been any research into this question?
Matthew 6.11 τὸν ἄρτον ἡμῶν τὸν ἐπιούσιον δὸς ἡμῖν σήμερον
Luke 11.3 τὸν ἄρτον ἡμῶν τὸν ἐπιούσιον δίδου ἡμῖν τὸ καθʼ ἡμέραν
IMHO, Matthew wrote first and Luke the used his work as a source--that's a minority opinion. Thus, Matthew invented the word and Luke retained it, although he slightly modified the phrase. That would make sense, as Matthew was a Jew and, as you mentioned, more likely to create a word based on some Aramaic construction. Luke may have been hesitant to modify the word, as its meaning wasn't absolutely clear.
The word itself is a compound of upon and substance, as in material belongings.
ἐπί can have temporal meanings; in particular, how long. It can also have the idea of repetition. This is speculation, but Matthew may have had both these ideas in mind: substance lasting a period of time (a day, from the context "today,") and repeatedly needed. Note that the word is an adjective describing "bread."
Thank you for bringing this up.
As for any research, Wikipedia has a good article on the word.