悠久
yōujiǔ · HSK 7
long in time
⏳ 悠 long-drawn-out + 久 a long time = stretching far back, ages and ages
The second character 久 already means a long duration; pair it with 悠 (distant, far-reaching) and you get the sense of time stretching across eras. Think of an old hourglass that never seems to run out.
久 — person 人 with a stroke marking the back
Originally a pictograph showing a person from behind with a mark indicating moxibustion treatment applied to the back, the original sense of 'cauterize' (now written 灸). It was borrowed phonetically to mean 'long time' or 'enduring,' which became its standard meaning.