空难
kōng nàn · HSK 7
air crash
✈️ 空 (air/sky) + 难 (disaster) = a disaster in the air, an air crash
空 means sky or air; 难 (nàn, falling tone) means calamity or disaster. Stack them and you get a calamity in the sky. Note 难 shifts to the 4th tone nàn for disaster, versus nán meaning difficult.
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.'
难 — 又 (right hand) + 隹 (short-tailed bird)
Originally written with 堇 (clay) plus 隹 (bird), 難 depicted a rare bird and was borrowed to mean 'difficult.' The modern simplified form replaces the left side with 又 (hand). The phonetic role of the original left component gave the reading nán.