密

It is a phono-semantic compound:

宀 (roof, house radical) – semantic element, suggesting something enclosed, covered, or hidden;

宓 (bok/mil, a surname, “quiet, calm”) – phonetic element;

山 (mountain) is also included in early forms, reinforcing the image of something enclosed or shut in.

Together, the character conveys the idea of “something enclosed and quiet under a roof - dense, secret, hidden.”

Semantic range:

- secret, hidden – confidential, not disclosed.

- dense, thick – as in dense forest, 密林.

- close, intimate – as in 친밀 (親密), close relationship.

- meticulous, precise – as in 세밀 (細密), fine, detailed.

비밀 (祕密/秘密) – secret

밀접 (密接) – close, intimate

밀실 (密室) – secret chamber

밀도 (密度) – density

친밀 (親密) – intimacy

In East Asia, 祕/秘 and 密 almost always appear together as 祕密 / 秘密, reinforcing the meaning “hidden and secret.”

密 itself often extends beyond secrecy to ideas of density, closeness, and precision.