The article points out that this word is effectively a hapax legomenon in Ancient Greek. It only shows up in this NT context, and not elsewhere. We can speculate about what it means from the surrounding text-- it appears to modify "bread"; its morphology-- it decomposes nicely into "over" + "being, essence"; and its parallels in other sources, but we'll never be sure what it means. It might just as well be a prayer for being sustained in abundance, and this might even be expected since people in the time of Jesus thought that the end times were at hand, and with those the "world to come" where the righteous would be rewarded. But even that is speculation.