Where does “día lúain” come from?

día lúain (Old Irish) comes from Latin dies Lūnae, from Ancient Greek σελήνη, from Ancient Greek Σέλας — light, brightness, the bright flame or blaze of fire.

Ancestry of “día lúain”, step by step

Step	Language	Word	Meaning
1	Latin	dies Lūnae	Monday
2	Ancient Greek	σελήνη	moon; month; a moon-shaped cake
3	Ancient Greek	Σέλας	light, brightness, the bright flame or blaze of fire

Every word from Ancient Greek Σέλας →Every word from Ancient Greek σελήνη →Every word from Latin dies Lūnae →