vault of heaven; vaulted sky
Poetic or literary term for the sky as a vast dome or arch. Rare in everyday conversation; found in classical or descriptive writing.
夜空を見上げると、穹窿に無数の星が輝いていた。
Looking up at the night sky, countless stars shone in the vault of heaven.
Architectural sense: a dome or arched vault. Also rare and literary; modern technical terms like ドーム or アーチ are more common.
Beautiful frescoes are painted on the vault of the church.
From Chinese 穹窿 (qiónglóng), meaning 'dome' or 'vault'. The kanji 穹 means 'sky' or 'vault', and 窿 means 'dome' or 'arch'. The exact historical derivation is uncertain; the spelling is conventionally associated with these meanings.