Where does “εἰᾰ́ν” come from?

εἰᾰ́ν (Ancient Greek) comes from Ancient Greek εἰ, from Proto-Indo-European h₁ey.

Ancestry of “εἰᾰ́ν”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	εἰ	if
2	Proto-Indo-European	h₁ey	—