空中
くうちゅう · kuuchuu · JLPT N2 · noun
sky
🪁 空 (sky, empty) + 中 (middle, inside) = the open space inside the sky = air
空 means sky or empty space, and 中 means middle or inside. Together, 空中 is the air inside the open sky, where kites and birds fly.
空 — cave radical 穴 + 工 (phonetic)
Originally a phono-semantic compound: 穴 (cave, hole) gives the meaning of emptiness or hollow space, while 工 supplies the sound. The earliest sense was 'hole' or 'cavity,' which extended to 'empty,' 'sky,' and 'in vain.' The reading kòng (4th tone) specifically means 'free time' or 'vacancy.'
中 — vertical stroke 丨 through enclosure 口
Pictograph of a banner or pole piercing the center of a target or territory, depicting the idea of 'middle' or 'center'. The horizontal frame represents boundaries, and the vertical line marks the central axis. The meaning extended from spatial center to 'middle, central, China' (中国, the Middle Kingdom).