noun
sky; the air; the heavens
The physical sky or the space above; also used in poetic or literary contexts for the heavens.
空がきれいに晴れている。
The sky is beautifully clear.
鳥が空を飛んでいる。
Birds are flying in the sky.
noun
Used in expressions like 空模様 (weather conditions) or 空が怪しい (the weather looks threatening).
今日は空がどんよりしている。
The weather is gloomy today.
noun
far-off place; distant place
Often used in set phrases like 空の果て (the ends of the earth) or 空遠く (far away).
彼は空の彼方へ旅立った。
He set off for a distant land.
noun
Appears in the pattern 〜空もない, meaning 'too preoccupied to notice anything else'.
彼女は恋に落ちて、勉強どころの空もない。
She's fallen in love and has no mind for studying.
noun
from memory; by heart
Used adverbially as 空で, meaning 'by heart' or 'from memory'.
彼は長い詩を空で言える。
He can recite a long poem from memory.
noun
Used in compounds like 空言 (そらごと, lie) or 空頼み (false hope). Rarely used alone.
それは空言に過ぎない。
That's nothing but a lie.
noun, used as a prefix
fake; pretended
Prefix-like use before nouns or verbs, indicating something false or pretended.
空泣きして同情を引こうとした。
He tried to gain sympathy by fake crying.
The word そら is native Japanese, with the kanji 空 (meaning 'empty' or 'sky') assigned to it. The historical derivation is uncertain.