dark, ocean
溟 centers on a vast, dark expanse of water: the deep ocean or sea, especially when it appears dark and mysterious.
溟 combines 氵 (water) with 冥, which likely contributes both sound and the idea of darkness or obscurity, together suggesting a dark sea.
Water 氵 beside 冥 (dark, obscure) creates the image of a dark, deep ocean where light barely reaches.
For メイ, imagine a dark ocean under a moonless May night: May -> メイ, and the sea is pitch black.