The Greek word here is epiousion, which is a hapax — a word that is only used here and nowhere else in the Greek language — and so presumed to be the Greek equivalent of whatever word Our Lord may have used in Aramaic or Hebrew. Most translate the word as “daily”, and this goes back to the Latin of Saint Jerome, who renders “arton epiousion” as “panis quotidianum”, daily bread, in the Gospel of Luke. However, in the Gospel of Saint Matthew, Jerome translates the same words as “panis supersubstantialem”. In other words, Jerome, who realized that this Greek hapax could not be expressed in Latin with both meanings at once, chose to give it one meaning in Matthew — “daily”; and another in Luke — “supersubstantial”, so as to preserve both senses of the word for Latin speaking Christians, albeit in two distinct biblical locations.