Meaning
宙 names the open expanse above and beyond us — mid-air, sky, space, cosmos. It also carries a sense of suspension: something hovering, unsupported, cut loose from the ground.
The kanji breaks into two parts. The top radical 宀 means "roof" or "shelter." The lower component 由 originally depicted a sprout pushing up through soil, suggesting origin or outward flow. Together they evoke a boundless expanse stretching beyond any roof — the sky, outer space, the cosmos itself.
In classical Chinese, 宙 specifically meant "duration" or "time," the temporal half of 宇宙 (universe), where 宇 covered space and 宙 covered time. Modern Japanese shifted the meaning: 宙 now points to space and mid-air rather than time.
宙 has 8 strokes, is taught in Grade 6, and sits at JLPT N2.
Readings
On'yomi (音読み) — Chinese-derived reading
The single On'yomi is チュウ (chuu). This is the only reading you'll encounter in practice — 宙 almost always appears inside compound words (熟語 — じゅくご), never standalone.
- 宇宙 (uchū) — universe, outer space
- 空中 (kūchū) — mid-air, in the air
- 宙返り (chūgaeri) — somersault, loop-the-loop
Kun'yomi (訓読み) — Native Japanese reading
宙 has no Kun'yomi in modern Japanese. "Sky" in everyday speech is 空 (sora); "inside/middle" is 中 (naka). Focus on the On'yomi チュウ and its compounds — that covers everything you need.
Common Words & Compounds
Universe & Space
- 宇宙 (uchū) — universe, cosmos. The standard word for outer space in Japanese.
- 宇宙飛行士 (uchū hikōshi) — astronaut, cosmonaut
- 宇宙船 (uchūsen) — spacecraft, spaceship
- 宇宙人 (uchūjin) — alien, extraterrestrial
- 宇宙開発 (uchū kaihatsu) — space exploration, space development
Mid-air & Suspension
- 空中 (kūchū) — mid-air. Anything airborne, not touching the ground.
- 宙に浮く (chū ni uku) — to float in mid-air; figuratively, to be left undecided
- 宙返り (chūgaeri) — somersault, aerial flip
- 宙づり (chūzuri) — hanging, suspended (with nothing supporting from below)
- 宙ぶらりん (chūburarin) — dangling in mid-air; in limbo, unresolved
Figurative & Poetic Uses
- 宙を見る (chū o miru) — to stare into space, to look blank (lost in thought)
- 宙に舞う (chū ni mau) — to dance through the air (leaves, snow, petals)
Example Sentences
宇宙はとても広いです。
Uchū wa totemo hiroi desu.
The universe is very vast.
彼は夢で宙に浮かんでいました。
Kare wa yume de chū ni ukande imashita.
He was floating in mid-air in his dream.
空中ブランコはとても興奮します。
Kūchū buranko wa totemo kōfun shimasu.
The trapeze is thrilling to watch.
将来、宇宙飛行士になりたいです。
Shōrai, uchū hikōshi ni naritai desu.
I want to become an astronaut someday.
サーカスの演者が見事な宙返りを披露した。
Sākasu no enja ga migoto na chūgaeri o hirō shita.
The circus performer pulled off a flawless somersault.
彼の計画は宙に浮いたまま、決まっていません。
Kare no keikaku wa chū ni uita mama, kimatte imasen.
His plan is still up in the air — nothing has been decided.
夜空に瞬く星々を見上げて、宇宙の神秘に思いをはせました。
Yozora ni matataku hoshiboshi o miagete, uchū no shinpi ni omoi o hasemashita.
Gazing up at the stars in the night sky, I found myself lost in the mystery of the cosmos.
部屋の真ん中に宙づりになったオブジェが、幻想的な雰囲気を醸し出していました。
Heya no mannaka ni chūzuri ni natta obuje ga, gensōteki na fun'iki o kamoshidashite imashita.
An object suspended in the middle of the room gave the space a dreamlike atmosphere.
Memory Tip
宀 is a roof. 由 shows something rising from the ground. Stack them: you're under a roof, watching something push upward — right through the ceiling and into open 宙.
Or flip it: the only reason (由) we build a roof (宀) is to shelter ourselves from what's above — the cold, open space (宙).