The Japanese noun 'キー (きー)' is a loanword from English, meaning 'key'. It is commonly used to refer to a physical key for unlocking doors or locks, as well as metaphorical keys, such as a key to success. In technology, it can also refer to keyboard keys or cryptographic keys. Example sentences: I lost my key「キーをなくした」(きーをなくした). The key to solving this problem is patience「この問題を解決するキーは忍耐だ」(このもんだいをかいけつするきーはにんたいだ).