空虚
kōng xū · HSK 7
emptiness
🕳️ 空 (empty/sky) + 虚 (void, unreal) = doubled emptiness, a hollow void
Both characters mean empty: 空 is the empty sky or hollow space, 虚 is the void or the false/unreal. Stacking two empties gives kōng xū, a hollowness so total it feels meaningless.
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.'
虚 — tiger radical 虍 + hill 丘 (now 业)
Originally depicted a large mound or hill where tigers (虍) roamed, written with 虍 over 丘. Because such high places were often deserted, the meaning shifted from 'big hill' to 'empty, void, vacant,' and by extension 'unreal' or 'humble.' The bottom 丘 was later simplified to 业.