Old Japanese *sora*, attested in the Man'yōshū (8th century). Scholars link it to the verb *soru* (to curve, to arch), evoking the vault of the sky arching overhead. The character 空 (OC *kʰoŋ*) was borrowed from Chinese, where it means "empty/void," but the underlying Japanese word predates that borrowing.

Sky imagery is deeply woven into Japanese aesthetics. The concept of *sora* appears constantly in haiku — Matsuo Bashō and other masters used shifting skies to anchor seasonal feeling (*kigo*). In modern Japanese, 空 doubles as a component in everyday compound words: 空港 (*kūkō*, airport), 空気 (*kūki*, air/atmosphere), and 青空 (*aozora*, blue sky — a symbol of freedom and hope). Note that when read *kū* (the on-yomi), the same kanji means "emptiness," a key concept in Buddhism.