İyi, relates to moon because of it is being at a sweet spot. Because substantial amount of Turkish language originates from Bakis figures. Sun is significant object in language development process. It is brightness source of natural light however it burns the eye. Moon is at sweet spot. Because of this phenomena it is very likely that “iyi" has a meaning like “sweet spot, moon like”. “Ay” means moon in Turkish. Actually the main reference for establishing similarities.
In English alphabet “y” and “i” are connected.