Realm (noun)

1. A particular sphere or area of activity or experience.
2. A kingdom or domain ruled by a monarch.
3. An area of knowledge or experience.

Origin:

Middle english (denoting royal power or sovereignty): from old french realme, from latin regnum 'kingdom, rule, reign'; later associated with royal + realm.

Examples:

1. The realm of science fiction includes books, movies, and video games set in imaginary worlds.
2. The kingdom was one of the largest and most prosperous in the realm.
3. She was recognized as an expert in the realm of renewable energy.
4. The realm of politics can be a complicated and messy place.
5. The realm of the supernatural was often explored in the old folktales.