Source : Webster's Revised Unabridged Dictionary (1913)

Realm \Realm\, n. [OE. realme, ream, reaume, OF. reialme,
   roialme, F. royaume, fr. (assumed) LL. regalimen, from L.
   regalis royal. See {Regal}.]
   1. A royal jurisdiction or domain; a region which is under
      the dominion of a king; a kingdom.

            The absolute master of realms on which the sun
            perpetually alone.                    --Motley.

   2. Hence, in general, province; region; country; domain;
      department; division; as, the realm of fancy.

Source : WordNet®

realm
     n 1: 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" [syn: {kingdom}, {land}]
     2: a knowledge domain that you are interested in or are
        communicating about; "it was a limited domain of
        discourse"; "here we enter the region of opinion"; "the
        realm of the occult" [syn: {domain}, {region}]
     3: the domain ruled by a king or queen [syn: {kingdom}]