The Collaborative International Dictionary of English v.0.48:

Organ \Or"gan\ ([^o]r"gan), n. [L. organum, Gr. 'o`rganon; akin
   to 'e`rgon 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.
      [1913 Webster]

   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.
      [1913 Webster]

   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.
         [1913 Webster]

   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.
      [1913 Webster]

   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. A newsletter distributed within an organization
      is often called its house organ.
      [1913 Webster +PJC]

   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 considered an organ.
      [1913 Webster]

            The deep, majestic, solemn organs blow. --Pope.
      [1913 Webster]

   Note: Chaucer used the form orgon as a plural.
         [1913 Webster]

               The merry orgon . . . that in the church goon
               [go].
         [1913 Webster]

   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 (Zool.), a Tasmanian crow shrike (Gymnorhina
      organicum). It utters discordant notes like those of a
      hand organ out of tune.

   Organ fish (Zool.), the drumfish.

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

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

   Organ of Corti (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. (Zool.) See Tubipora.

   Organ point (Mus.), a passage in which the tonic or
      dominant is sustained continuously by one part, while the
      other parts move.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Organ \Or"gan\, v. t.
   To supply with an organ or organs; to fit with organs; to
   organize. [Obs.]
   [1913 Webster]

         Thou art elemented and organed for other apprehensions.
                                                  --Bp.
                                                  Mannyngham.
   [1913 Webster] Organdie

WordNet (r) 3.0 (2006):

organ
    n 1: a fully differentiated structural and functional unit in an
         animal that is specialized for some particular function
    2: a government agency or instrument devoted to the performance
       of some specific function; "The Census Bureau is an organ of
       the Commerce Department"
    3: (music) an electronic simulation of a pipe organ [syn:
       electric organ, electronic organ, Hammond organ,
       organ]
    4: a periodical that is published by a special interest group;
       "the organ of the communist party"
    5: wind instrument whose sound is produced by means of pipes
       arranged in sets supplied with air from a bellows and
       controlled from a large complex musical keyboard [syn:
       organ, pipe organ]
    6: a free-reed instrument in which air is forced through the
       reeds by bellows [syn: harmonium, organ, reed organ]

Moby Thesaurus II by Grady Ward, 1.0:

129 Moby Thesaurus words for "organ":
   Charlie McCarthy, Hammond organ, affiliate, agency, agent, ancilla,
   annual, appendage, appliance, arm, baroque organ, bimonthly,
   biweekly, bough, branch, branch office, calliope, calliophone,
   channel, chapter, choralcelo, component, contrivance, creature,
   daily, daybook, device, diary, division, dummy, dupe,
   electric organ, electro-pneumatic organ, element, ephemeris,
   fortnightly, forum, gazette, go-between, hand, handmaid,
   handmaiden, harmonium, hebdomadal, hydraulic organ, imp, implement,
   instrument, instrumentality, instrumentation, interagent,
   intermediary, intermediate, intermedium, joint, journal, leg,
   lever, limb, link, lobe, lobule, local, lodge, magazine, mean,
   mechanism, mediator, medium, melodeon, melodica, member, midwife,
   minion, ministry, monthly, mouthpiece, newsletter, newsmagazine,
   newspaper, offshoot, orchestrelle, organophone, paper, part, pawn,
   periodical, pictorial, pinion, pipe organ, plaything, post,
   process, publication, puppet, quarterly, ramification, reed organ,
   review, runner, scion, seraphine, serial, servant, slave,
   slick magazine, spray, sprig, spur, steam organ, stooge, structure,
   switch, symphonion, tail, tendril, tool, toy, tracker-action organ,
   trade magazine, tubular-pneumatic organ, twig, unit, vehicle,
   vocalion, voice, weekly, wing, yearbook



Easton's 1897 Bible Dictionary:

Organ
   some kind of wind instrument, probably a kind of Pan's pipes
   (Gen. 4:21; Job 21:12; Ps. 150:4), which consisted of seven or
   eight reeds of unequal length.