also: なかぞら
noun which may take the genitive case particle 'no', noun
Only with reading ちゅうくう
Describes something that is empty inside; used attributively with の. Reading restricted to ちゅうくう.
この柱は中空になっている。
This pillar is hollow inside.
風船が中空に浮かんでいる。
A balloon is floating in mid-air.
中空の雲がゆっくり流れていく。
Clouds in the sky are drifting slowly.
空中 is the more common word for 'in the air' or 'aerial'; 中空 is less frequent and can also mean 'hollow'.
Compound of 中 (middle) and 空 (sky, empty). The 'hollow' sense derives from the literal meaning 'empty inside', while the 'mid-air' sense comes from 'middle of the sky'.