Source : Webster's Revised Unabridged Dictionary (1913)

Domain \Do*main"\, n. [F. domaine, OF. demaine, L. dominium,
   property, right of ownership, fr. dominus master, owner. See
   {Dame}, and cf {Demesne}, {Dungeon}.]
   1. Dominion; empire; authority.

   2. The territory over which dominion or authority is exerted;
      the possessions of a sovereign or commonwealth, or the
      like. Also used figuratively.

            The domain of authentic history.      --E. Everett.

            The domain over which the poetic spirit ranges. --J.
                                                  C. Shairp.

   3. Landed property; estate; especially, the land about the
      mansion house of a lord, and in his immediate occupancy;
      demesne. --Shenstone.

   4. (Law) Ownership of land; an estate or patrimony which one
      has in his own right; absolute proprietorship; paramount
      or sovereign ownership.

   {Public domain}, the territory belonging to a State or to the
      general government; public lands. [U.S.]

Source : WordNet®

domain
     n 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" [syn: {sphere}, {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" [syn: {demesne}, {land}]
     3: the set of values of the independent variable for which a
        function is defined
     4: people in general; especially a distinctive group of people
        with some shared interest; "the Western world" [syn: {world}]
     5: 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: {region}, {realm}]

Source : Free On-Line Dictionary of Computing

domain
     
        1.  In the theory of functions, the set of
        argument values for which a {function} is defined.
     
        See {domain theory}.
     
        2.  A group of computers whose {hostnames} share a
        common suffix, the "domain name".  The last component of this
        is the {top-level domain}.
     
        See {administrative domain}, {Domain Name System}, {fully
        qualified domain name}.
     
        3. {Distributed Operating Multi Access Interactive Network}.
     
        4.  A specific phase of the {software life cycle}
        in which a developer works.  Domains define developers' and
        users' areas of responsibility and the scope of possible
        relationships between products.
     
        5. The subject or market in which a piece of software is
        designed to work.
     
        (1997-12-26)