宙
zhoù · HSK 7
eternity
宀 roof + 由 (you, cause); the 由 part also hints the zhòu sound — span of all time
宙 pairs with 宇 in 宇宙 (universe): 宇 is all space, 宙 is all time. The 宀 roof radical frames it as a vast container, while 由 supplies a phonetic clue close to zhòu.
宙 — roof 宀 + 由 (phonetic)
宙 is a semantic-phonetic compound: the roof radical 宀 suggests space or dwelling, while 由 supplies the sound. Originally referring to the ridgepole of a roof, it came to mean 'time' or 'eternity,' and pairs with 宇 (space) in 宇宙 'universe.'