Source : Webster's Revised Unabridged Dictionary (1913)

Organ \Or"gan\, n. [L. organum, Gr. ?; akin to ? work, and E.
   work: cf. F. organe. See {Work}, and cf. {Orgue}, {Orgy}.]
   1. An instrument or medium by which some important action is
      performed, or an important end accomplished; as,
      legislatures, courts, armies, taxgatherers, etc., are
      organs of government.

   2. (Biol.) A natural part or structure in an animal or a
      plant, capable of performing some special action (termed
      its function), which is essential to the life or
      well-being of the whole; as, the heart, lungs, etc., are
      organs of animals; the root, stem, foliage, etc., are
      organs of plants.

   Note: In animals the organs are generally made up of several
         tissues, one of which usually predominates, and
         determines the principal function of the organ. Groups
         of organs constitute a system. See {System}.

   3. A component part performing an essential office in the
      working of any complex machine; as, the cylinder, valves,
      crank, etc., are organs of the steam engine.

   4. A medium of communication between one person or body and
      another; as, the secretary of state is the organ of
      communication between the government and a foreign power;
      a newspaper is the organ of its editor, or of a party,
      sect, etc.

   5. [Cf. AS. organ, fr. L. organum.] (Mus.) A wind instrument
      containing numerous pipes of various dimensions and kinds,
      which are filled with wind from a bellows, and played upon
      by means of keys similar to those of a piano, and
      sometimes by foot keys or pedals; -- formerly used in the
      plural, each pipe being considired an organ.

            The deep, majestic, solemn organs blow. --Pope.

   Note: Chaucer used the form orgon as a plural.

               The merry orgon . . . that in the church goon
               [go].

   {Barrel organ}, {Choir organ}, {Great organ}, etc. See under
      {Barrel}, {Choir}, etc.

   {Cabinet organ} (Mus.), an organ of small size, as for a
      chapel or for domestic use; a reed organ.

   {Organ bird} (Zo["o]l.), a Tasmanian crow shrike ({Gymnorhina
      organicum}). It utters discordant notes like those of a
      hand organ out of tune.

   {Organ fish} (Zo["o]l.), the drumfish.

   {Organ gun}. (Mil.) Same as {Orgue}
      (b) .

   {Organ harmonium} (Mus.), an harmonium of large capacity and
      power.

   {Organ of Gorti} (Anat.), a complicated structure in the
      cochlea of the ear, including the auditory hair cells, the
      rods or fibers of Corti, the membrane of Corti, etc. See
      Note under {Ear}.

   {Organ pipe}. See {Pipe}, n., 1.

   {Organ-pipe coral}. (Zo["o]l.) See {Tubipora}.

   {Organ point} (Mus.), a passage in which the tonic or
      dominant is sustained continuously by one part, while the
      other parts move.



   4. A metallic tube, as of a gun, from which a projectile is
      discharged. --Knight.

   5. A jar. [Obs.] --1 Kings xvii. 12.

   6. (Zo["o]l.) The hollow basal part of a feather.

   {Barrel bulk} (Com.), a measure equal to five cubic feet,
      used in estimating capacity, as of a vessel for freight.
      

   {Barrel drain} (Arch.), a drain in the form of a cylindrical
      tube.

   {Barrel of a boiler}, the cylindrical part of a boiler,
      containing the flues.

   {Barrel of the ear} (Anat.), the tympanum, or tympanic
      cavity.

   {Barrel organ}, an instrument for producing music by the
      action of a revolving cylinder.

   {Barrel vault}. See under {Vault}.

Source : WordNet®

barrel organ
     n : a musical instrument that makes music by rotation of a
         cylinder studded with pegs [syn: {grind organ}, {hand
         organ}, {hurdy gurdy}, {street organ}]