PREDATOR

If the word was missing from the sentence, then it could be translated as “Give us today our bread and forgive our sins…”.

Instead, with the word added, it can be translated as "Give us today the bread we need for the day and forgive our sins… ".

I guess the significance of the word is in not being greedy and asking from God only what you really need instead of what is “owed” to you?

Greek guy here.

Επιούσιος (e-pi-u-si-os) is a composite word (you can make an astronomical number of composite words in Greek if you want to express a new concept, such as tele-phone) and in this sentence it means that which will nourish us for the day. So daily is quite fitting here.