空

1. noun sky; the air; the heavens
2. weather
3. far-off place; distant place
4. often as 〜空もない state of mind; feeling
5. usu. as 空で (from) memory; (by) heart
6. falsehood; lie
7. prefix, before an adjective somehow; vaguely
8. before a noun or a verb fake

から

1. noun, takes の emptiness; being empty
2. prefix not carrying anything; unburdened; empty-handed
3. dishonoured (bill, promise, etc.); false; no-show (reservation); put-on (cheeriness, courage, etc.); empty (compliments); insincere

うろ · うつお · うつほ · うつせ also 虚 · 洞

1. noun hollow; cavity; hole

くう

1. noun empty air; sky
2. Buddhism shunyata (the lack of an immutable intrinsic nature within any phenomenon); emptiness
3. abbreviation air force
4. noun, na-adjective fruitlessness; meaninglessness
5. void (one of the five elements)
6. takes の, mathematics empty (e.g. set)