domain in WordNet English dictionary

1. a particular environment or walk of life
   "his social sphere is limited"; "it was a closed area of employment"; "he's out of my orbit"
   sphere  domain  area  orbit  field  arena 
   
2. territory over which rule or control is exercised
   "his domain extended into Europe"; "he made it the law of the land"
   domain  demesne  land 
   
3. the content of a particular field of knowledge
   knowledge domain  knowledge base  domain 
   
4. people in general; especially a distinctive group of people with some shared interest
   "the Western world"
   world  domain 
   
5. (mathematics) the set of values of the independent variable for which a function is defined
   domain  domain of a function