幽
ユウ, ヨウ, ふか.い, かす.か, くら.い, しろ.い
seclude, confine to a room, deep, profound, secluded, faint, dark, tranquil, calm
JLPT1 G7 S9 F1996
An element# doubling 幺 slender thread (→ slight, obscure objects) + 山 mountain → obscure, remote mountain, *far removed from human habitation* → *unknown*; *deep*; *dark*; *profound*; *faint* → *afterlife*.
[Full Kanji Etymology List]