Source : Webster's Revised Unabridged Dictionary (1913)

Union \Un"ion\ (?; 277), n. [F., from L. unio oneness, union, a
   single large pearl, a kind of onion, fr. unus one. See {One},
   and cf. {Onion}, {Unit}.]
   1. The act of uniting or joining two or more things into one,
      or the state of being united or joined; junction;
      coalition; combination.

   Note: Union differs from connection, as it implies that the
         bodies are in contact, without an inter?ening body;
         whereas things may be connected by the in???vention of
         a third body, as by a cord or chain.

   2. Agreement and conjunction of mind, spirit, will,
      affections, or the like; harmony; concord.

   3. That which is united, or made one; something formed by a
      combination or coalition of parts or members; a
      confederation; a consolidated body; a league; as, the
      weavers have formed a union; trades unions have become
      very numerous; the United States of America are often
      called the Union. --A. Hamilton.

   4. A textile fabric composed of two or more materials, as
      cotton, silk, wool, etc., woven together.

   5. A large, fine pearl. [Obs.]

            If they [pearls] be white, great, round, smooth, and
            weighty . . . our dainties and delicates here at
            Rome . . . call them unions, as a man would say
            ``singular,'' and by themselves alone. --Holland.

            In the cup an union shall he throw, Richer than that
            which four successive kings In Denmark's crown have
            worn.                                 --Shak.

   6. A device emblematic of union, used on a national flag or
      ensign, sometimes, as in the military standard of Great
      Britain, covering the whole field; sometimes, as in the
      flag of the United States, and the English naval and
      marine flag, occupying the upper inner corner, the rest of
      the flag being called the fly. Also, a flag having such a
      device; especially, the flag of Great Britain.

   Note: The union of the United States ensign is a cluster of
         white stars, denoting the union of the States, and,
         properly, equal in number to that of the States,
         displayed on a blue field; the fly being composed of
         alternate stripes of red and white. The union of the
         British ensign is the three crosses of St. George, St.
         Andrew, and St. Patrick in combination, denoting the
         union of England, Scotland and Ireland, displayed on a
         blue field in the national banner used on shore, on a
         red, white, or blue field in naval ensigns, and with a
         white border or fly in the merchant service.



   7. (Mach.) A joint or other connection uniting parts of
      machinery, or the like, as the elastic pipe of a tender
      connecting it with the feed pipe of a locomotive engine;
      especially, a pipe fitting for connecting pipes, or pipes
      and fittings, in such a way as to facilitate
      disconnection.

   8. (Brewing) A cask suspended on trunnions, in which
      fermentation is carried on.

   {Hypostatic union} (Theol.) See under {Hypostatic}.

   {Latin union}. See under {Latin}.

   {Legislative Union} (Eng. Hist.), the union of Great Britain
      and Ireland, which took place Jan. 1, 1801.

   {Union}, or {Act of Union} (Eng. Hist.), the act by which
      Scotland was united to England, or by which the two
      kingdoms were incorporated into one, in 1707.

   {Union by the first}, or {second}, {intention}. (Surg.) See
      {To heal by the first, or second, intention}, under
      {Intention}.

   {Union down} (Naut.), a signal of distress at sea made by
      reversing the flag, or turning its union downward.

   {Union jack}. (Naut.) See {Jack}, n., 10.

   {Union joint}. (Mech.)
      (a) A joint formed by means of a union.
      (b) A piece of pipe made in the form of the letter T.

   Syn: Unity; junction; connection; concord; alliance;
        coalition; combination; confederacy.

   Usage: {Union}, {Unity}. Union is the act of bringing two or
          more things together so as to make but one, or the
          state of being united into one. Unity is a state of
          simple oneness, either of essence, as the unity of
          God, or of action, feeling, etc., as unity of design,
          of affection, etc. Thus, we may speak of effecting a
          union of interests which shall result in a unity of
          labor and interest in securing a given object.

                One kingdom, joy, and union without end.
                                                  --Milton.

                [Man] is to . . . beget Like of his like, his
                image multiplied. In unity defective; which
                requires Collateral love, and dearest amity.
                                                  --Milton.

Source : WordNet®

Union
     adj 1: being of or having to do with the northern United States and
            those loyal to the Union during the Civil War; "Union
            soldiers"; "Federal forces"; "a Federal infantryman"
            [syn: {Federal}]
     2: of trade unions; "the union movement"; "union negotiations";
        "a union-shop clause in the contract" [ant: {nonunion}]

Source : Free On-Line Dictionary of Computing

union
     
        1.  An operation on two {sets} which returns the
        set of all elements that are a member of either or both of the
        argument sets; normally written as an infix upper-case U
        symbol.  The operator generalises to zero or more sets by
        taking the union of the current partial result (initially the
        empty set) with the next argument set, in any order.
     
        For example, (a, b, c) U (c, d, e) = (a, b, c, d, e)
     
        2.  A {type} whose values may be of one of a
        number of other types, thet current type depending on
        conditions that are only known at {run-time}.  A {variable} of
        union type must be allocated sufficient storage space to hold
        the largest component type.  Some unions include extra
        information to say which type of value the union currently has
        (a "tagged union"), others rely on the program to keep track
        of this independently.
     
        A union contrasts with a {structure} or {record} which stores
        values of all component types at once.
     
        3.  An {SQL} {operator} that concatenates two result
        sets, that must have the same number and types of {columns}.
        The operator may be followed by the word "ALL" to indicate
        that results that appear in both sets should appear twice in
        the output.
     
        (2002-02-26)