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empty air; sky
fruitlessness; meaninglessness
shunyata (the lack of an immutable intrinsic nature within any phenomenon); emptiness
air force
void (one of the five elements)
empty (e.g. set)
「空」 has other readings with different meanings.
空を切るように手を振った。
I waved my hand as if cutting through the air.
ボールが空高く上がっていった。
The ball went high up into the sky.
空に向かって大きな声で叫んでみたかった。
I wanted to shout loudly toward the sky.