realm

(noun) a domain in which something is dominant. Synonyms: kingdom, land. Examples: "The untroubled kingdom of reason." "A land of make-believe." "The rise of the realm of cotton in the south."

(noun) the domain ruled by a king or queen. Synonyms: kingdom.

(noun) a knowledge domain that you are interested in or are communicating about. Synonyms: region. Examples: "It was a limited realm of discourse." "Here we enter the region of opinion." "The realm of the occult."