noun
blue sky; open sky
Literally a ceiling painted or imagined as a blue sky; also used for an open-air ceiling or the sky itself.
温泉の露天風呂は青天井で、とても気持ちがいい。
The open-air hot spring bath has an open sky above, and it feels wonderful.
noun
skyrocketing; unlimited; the sky's the limit
Idiomatic expression for prices, costs, or values that rise without an upper bound. Often used in financial or economic contexts.
このままでは医療費が青天井で上がり続ける。
At this rate, medical costs will keep skyrocketing without limit.
仮想通貨の価格は青天井だ。
The price of cryptocurrency is unlimited; the sky's the limit.