冥
メイ, ミョウ, くら.い
dark
JLPT0 G7 S10 F2349
In its present form, 冖# cover + an element combining 日 sun/day + 六 (originally, 入 enter) → cover blocking the entry of sunlight → *darkness* → *the depths*; *the other world* (← unseen dimension). Also, *stupidity* (← dark ignorance). However, 冥 itself is likely the source of the 冖 element/character, suggesting that a different combination of elements conveyed the idea of darkness in the earliest form of 冥.
[Full Kanji Etymology List]