black and shining, ebony
黟 centers on a deep, lustrous black, like polished ebony wood. The given meanings describe the same visual quality: a black surface that shines.
黟 combines 黑 (black) with 多, which likely contributes the sound. The character was used historically for a place name and for the idea of shiny black.
The left side 黑 gives the black color, and the right side 多 (many) suggests an abundance of that blackness—so much black that it becomes glossy and shining, like many layers of polished ebony.
For エイ, picture a shiny black 'A' grade ebony: 'A' -> エイ, the finest ebony with a deep, lustrous black.