永久
yǒng jiǔ · HSK 7
forever
♾️ 永 (eternal) + 久 (long-lasting) = a long time that never ends, forever
永 carries the sense of eternal and 久 means a long duration; stack them and you get permanence. Tied to the river radical in 永, once meaning a long unbroken flow of water that never stops.
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.