realm in WordNet English dictionary

1. the domain ruled by a king or queen
   kingdom  realm 
   
2. a domain in which something is dominant
   "the untroubled kingdom of reason"; "a land of make-believe"; "the rise of the realm of cotton in the south"
   kingdom  land  realm 
   
3. a knowledge domain that you are interested in or are communicating about
   "it was a limited realm of discourse"; "here we enter the region of opinion"; "the realm of the occult"
   region  realm