Select the most appropriate meaning of the given idiom.

On cloud nine

Extremely happy

The most appropriate meaning of the idiom "on cloud nine" is >Extremely happy.<

This idiom is used to describe someone who is feeling very happy and content. The image of being on a cloud is a metaphor for being in a state of bliss or euphoria.

The idiom is thought to have originated in the 1950s, and it is believed to be a reference to the cumulonimbus cloud, which is the highest type of cloud and is often associated with thunderstorms. However, the idiom is not actually related to weather or clouds.

For example, you might say that someone is on cloud nine after they get married or win the lottery.

The other options are not correct.

• Good number: The number 9 is considered to be a lucky number in some cultures, but it is not associated with the idiom "on cloud nine".
• Travel by airplane: While being on an airplane can be a happy experience for some people, it is not the literal meaning of the idiom.
• Heavy rain: Clouds can bring rain, but they are not the literal meaning of the idiom.