悠

A phono-semantic compound composed of:

心 — semantic component meaning “heart; mind”; 攸 — phonetic component indicating the sound (유 / yōu). The character expresses a state of mind that is distant, calm, or unhurried.
Semantic development: - distant or far away; - long-lasting or enduring; - calm, relaxed, or leisurely state of mind.

유유 (悠悠) — distant; boundless; leisurely

유구 (悠久) — long-lasting; eternal

유구한 역사 (悠久한 歷史) — a long and enduring history

悠 often appears in literary expressions describing vast time spans, calm emotions, or elegant atmosphere. Reduplicated forms such as 悠悠 emphasize great distance or long duration.
Related characters: 遠 — far

久 — long time

閑 — leisure

思 — to think

These characters relate to distance, time, and calm mental states.