Meaning
The kanji 空 holds two meanings that are more connected than they first appear: sky and emptiness. Look up at a vast, open sky and you are looking into an enormous, boundless void stretching above you. Sky and emptiness are the same thing seen from different angles — and 空 carries both senses at once.
Visually, the character is composed of two parts: 穴 (あな, ana) meaning hole or cave on top, and 工 (こう, kou) meaning craft or construction below. The idea of a craftsman hollowing out a space — creating emptiness — gives this kanji its core sense of a void or opening. Extend that void upward infinitely, and you get the sky.
This kanji is taught in Grade 1 of Japanese elementary school, making it one of the very first kanji Japanese children learn. It has 8 strokes and belongs to the radical 穴 (hole). For Vietnamese learners, the Hán-Việt reading is KHÔNG — the same root found in không gian (空間, space), không khí (空気, air/atmosphere), and the philosophical hư không (emptiness, nothingness). The pronunciation and meaning both carry over directly.
In everyday Japanese, 空 appears constantly. You look up at the sora (sky), arrive at the airport (kuukou), breathe the kuuki (air), and even practice karate (空手, "empty hand"). Few kanji show up in so many corners of daily life.
Readings
On'yomi (音読み) — Chinese-derived readings
The on'yomi readings コウ and クウ both appear in compound words (熟語, jukugo) and derive from the Chinese pronunciation. クウ is more common in modern Japanese and tends to appear in words related to air, emptiness, or aviation.
- 空気 (kuuki) — air, atmosphere. The air you breathe every moment of the day.
- 空港 (kuukou) — airport. Literally "air harbor" — a port for the sky.
- 空間 (kuukan) — space, void. The empty space around us.
- 空腹 (kuufuku) — hunger. Literally "empty stomach" — a vivid way to describe being hungry.
- 航空 (koukuu) — aviation, air travel. Here 航 (こう) means to navigate or sail, and 空 is read クウ, meaning air — together: navigating through the air.
- 空想 (kuusou) — daydream, fantasy. Literally "empty thoughts" — thoughts drifting upward with nothing to anchor them.
Kun'yomi (訓読み) — Native Japanese readings
Kun'yomi readings are used for standalone words and reflect native Japanese vocabulary. そら is the most commonly used reading and one of the first words beginners encounter. から and あ.く both convey emptiness or vacancy.
- 空 (sora) — the sky. This is the everyday word for the sky you see when you look up.
- 青空 (aozora) — blue sky. One of the most beloved words in Japanese poetry and song.
- 夜空 (yozora) — night sky. An evocative word used in countless Japanese songs.
- 空 (kara) — empty (as a noun/prefix). Used to describe containers or situations with nothing inside.
- 空っぽ (karappo) — completely empty. The っぽ suffix makes it more colloquial and emphatic.
- 空手 (karate) — karate. Literally "empty hand" — the martial art that uses no weapons.
- 空く (aku) — to become empty or vacant. Used for seats, time slots, and spaces that open up.
- 空ける (akeru) — to empty out, to make a space available.
Common Words & Compounds
空 appears in a wide range of compound words. Below are some of the most useful, grouped by theme:
Sky & Nature
- 空 (sora) — the sky
- 青空 (aozora) — blue sky
- 夜空 (yozora) — night sky
- 空飛ぶ (sora tobu) — to fly through the sky
- 空模様 (sora moyou) — appearance of the sky, weather
Air & Aviation
- 空気 (kuuki) — air, atmosphere
- 空港 (kuukou) — airport
- 航空 (koukuu) — aviation
- 空軍 (kuugun) — air force
Emptiness & Vacancy
- 空白 (kuuhaku) — blank space, gap
- 空間 (kuukan) — space, void
- 空っぽ (karappo) — completely empty
- 空き缶 (akikan) — empty can
- 空き家 (akiya) — vacant house
- 空腹 (kuufuku) — hunger (empty stomach)
Abstract & Cultural
- 空手 (karate) — karate (empty hand)
- 空想 (kuusou) — daydream, fantasy
- 空虚 (kuukyo) — emptiness, hollowness (emotional)
Example Sentences
今日の空はとても青いです。
Kyou no sora wa totemo aoi desu.
Today's sky is very blue.
空気がきれいですね。
Kuuki ga kirei desu ne.
The air is clean, isn't it?
空港まで何分かかりますか？
Kuukou made nanpun kakarimasu ka?
How many minutes does it take to get to the airport?
この席は空いていますか？
Kono seki wa aite imasu ka?
Is this seat vacant?
冷蔵庫が空っぽです。
Reizouko ga karappo desu.
The refrigerator is completely empty.
夜空に星がたくさん見えます。
Yozora ni hoshi ga takusan miemasu.
You can see many stars in the night sky.
空腹なので、何か食べたいです。
Kuufuku na node, nanika tabetai desu.
Because I'm hungry, I want to eat something.
彼女はいつも空想にふけっています。
Kanojo wa itsumo kuusou ni fukette imasu.
She is always lost in daydreams.
飛行機が青い空を飛んでいます。
Hikouki ga aoi sora wo tonde imasu.
An airplane is flying through the blue sky.
空白に名前を書いてください。
Kuuhaku ni namae wo kaite kudasai.
Please write your name in the blank space.
Related Kanji
- 気 — Spirit, Energy, Air (Kanji N5)
- 木 — Tree, Wood (Kanji N5)
- 百 — Hundred (Kanji N5)
- 人 — Person (Kanji N5)
- 水 — Water (Kanji N5)
- 上 — Above, Up (Kanji N5)
Memory Tip
Picture a cave (穴) with a worker (工) inside, digging and hollowing it out. As the worker digs deeper, the cavity grows larger — until the ceiling breaks open and suddenly there is nothing above but open sky. What started as a small hollow became the boundless expanse of the heavens. Hold that image of looking up through the opening, and the two meanings of 空 — empty and sky — will stay connected in your memory.