The Japanese noun '鍵 (かぎ)' means 'key'. It refers to a physical object used to lock or unlock something, such as a door, a safe, or a car. This word is commonly used in everyday situations. For example: I lost my key「鍵をなくしました」(かぎをなくしました). Do you have the key to this door?「このドアの鍵を持っていますか?」(このドアのかぎをもっていますか?). Additionally, '鍵' can also metaphorically refer to something essential or crucial, as in 'the key to success' (成功の鍵, せいこうのかぎ).