宇宙
うちゅう · uchuu · JLPT N3 · noun
universe
🪐🌌 宇 = all of space + 宙 = all of time → the universe
An old Chinese text, the Huainanzi, defines 宇 as the four directions plus up and down, and 宙 as all time from past to present. Put all space and all time together and you get the cosmos. Both kanji carry the roof radical 宀.
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.'