空隙
kòng xì · HSK 7
gap between two objects
🪟 空 (empty) + 隙 (crack/crevice) = an empty crack, a gap between things
空 carries the sense of empty or hollow space; 隙 means a chink or crevice. Together they name the empty slot between two objects, or the free stretch of time between two events.
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.'