空気
くうき · kuuki · JLPT N4 · noun
air
🎈 空気 = empty (空) + spirit/gas (気): the invisible stuff filling empty space
空 means sky or empty; 気 means spirit, gas, or mood (as in 元気, 天気). Together: the gas of the sky. It also means social atmosphere — 空気を読む, to read the air, is sensing the unspoken mood of a room.
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.'