The Collaborative International Dictionary of English v.0.48:

Dummy \Dum"my\, a. [See Dumb.]
   1. Silent; mute; noiseless; as a dummy engine.
      [1913 Webster]

   2. Fictitious or sham; feigned; as, a dummy watch.
      [1913 Webster]

   Dummy car. See under Car.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dummy \Dum"my\, n.; pl. Dummies.
   1. One who is dumb. --H. Smith.
      [1913 Webster]

   2. A sham package in a shop, or one which does not contain
      what its exterior indicates.
      [1913 Webster]

   3. An imitation or copy of something, to be used as a
      substitute; a model; a lay figure; as, a figure on which
      clothing is exhibited in shop windows; a blank paper copy
      used to show the size of the future book, etc.
      [1913 Webster]

   4. (Drama) One who plays a merely nominal part in any action;
      a sham character.
      [1913 Webster]

   5. A thick-witted person; a dolt. [Colloq.]
      [1913 Webster]

   6. (Railroad) A locomotive with condensing engines, and,
      hence, without the noise of escaping steam; also, a dummy
      car.
      [1913 Webster]

   7. (Card Playing) The fourth or exposed hand when three
      persons play at a four-handed game of cards.
      [1913 Webster]

   8. A floating barge connected with a pier. --Knight.
      [1913 Webster]

   To play dummy, to play the exposed or dummy hand in cards.
      The partner of the dummy plays it. Dumose

WordNet (r) 3.0 (2006):

dummy
    adj 1: having the appearance of being real but lacking capacity
           to function; "a dummy corporation"
    n 1: a person who does not talk [syn: dummy, silent person]
    2: an ignorant or foolish person [syn: dumbbell, dummy,
       dope, boob, booby, pinhead]
    3: a figure representing the human form
    4: a cartridge containing an explosive charge but no bullet
       [syn: blank, dummy, blank shell]
    v 1: make a dummy of; "dummy up the books that are to be
         published" [syn: dummy, dummy up]

Moby Thesaurus II by Grady Ward, 1.0:

380 Moby Thesaurus words for "dummy":
   Boeotian, Charlie McCarthy, Intertype, Linotype, Monotype,
   a nobody, a nothing, ace, adherent, advocate, affected, agent,
   alter ego, alternate, alternative, amicus curiae, analogy, ancilla,
   apocryphal, appliance, artificial, ass, assumed, attorney, backup,
   backup man, bastard, best bower, block, blockhead, bogus, bower,
   brummagem, burlesque, bust, cards, carving, champion, change,
   changeling, cheat, cipher, clay model, clinquant, clod, clubs,
   cold-type typesetting, colorable, colored, common man, comparison,
   composing, composing stick, composition, computerized typesetting,
   contrivance, copy, counterfeit, counterfeited, creature, deaf-mute,
   deck, deputy, deuce, device, diamonds, dimwit, disciple, distorted,
   doll, dolly, dolt, donkey, dope, double, dressed up, dud, dullard,
   dullhead, dumb cluck, dumbbell, dummkopf, dunce, dupe, duplication,
   embellished, embroidered, equal, equivalent, ersatz, exchange,
   executive officer, exponent, face cards, facsimile, factitious,
   fake, faked, fakement, false, falsified, fantoccini, feigned,
   fictitious, fictive, figure, figurehead, figurine, fill-in, flunky,
   flush, follower, fool, forgery, frame-up, fraud, front, front man,
   full house, furniture, galley chase, garbled, ghost, ghostwriter,
   gillie, gingerbread man, go-between, goon, gowk, hand, handmaid,
   handmaiden, hanger-on, hearts, henchman, hoax, hollow man,
   hot-metal typesetting, idiot, ignoramus, illegitimate, imitation,
   implement, imposition, impostor, insignificancy, instrument,
   interagent, intermediary, intermediate, intermedium, jack, jackal,
   jackstraw, jobbernowl, joker, junk, junky, justification, king,
   knave, knockoff, lackey, lackwit, lamebrain, lay figure, layout,
   left bower, lever, lieutenant, lightweight, likeness, line of type,
   little fellow, little guy, locum, locum tenens, looby, loon,
   make-believe, makeshift, man, man of straw, man-made, manikin,
   mannequin, mannikin, marionette, mechanism, mediator, mediocrity,
   medium, metaphor, metonymy, midwife, minion, mock, mock-up, model,
   monument, moron, mute, myrmidon, nebbish, next best thing, niais,
   nincompoop, ninny, ninnyhammer, nitwit, nobody, nobody one knows,
   noddy, nominal head, nonentity, nothing, nullity, numskull,
   obscurity, organ, pacifier, pack, pair, paranymph, paraphrase,
   parody, paste, pawn, personnel, perverted, phony, photocomposition,
   photosetting, phototypesetter, phototypesetting machine,
   picture cards, pilot model, pinch, pinch hitter, pinchbeck,
   pip-squeak, playing cards, plaything, pleader, portrait bust,
   pretended, procurator, provisional, proxy, pseudo, punk, puppet,
   pushover, put, put-on, put-up job, quasi, queen, queer, quoin,
   relief, replacement, replica, representation, representative,
   reprint, reproduction, reserve, reserves, ringer, rip-off, round,
   royal flush, rubber, ruff, runt, sample, satellite, scarecrow,
   scrub, sculpture, second in command, second string, secondary,
   self-styled, servant, setting, sham, shoddy, shrimp, sign,
   simpleton, simulacrum, simulated, simulation, singleton, slave,
   slug, small fry, small potato, small potatoes, snowman, so-called,
   soi-disant, spades, spare, spares, spurious, squirt, squit,
   stand-in, statuary, statue, statuette, stooge, stopgap, straight,
   stupid, sub, substituent, substitute, substitution, succedaneum,
   superseder, supplanter, supposititious, surrogate, swindle,
   sycophant, symbol, synecdoche, synthetic, tentative, thickwit,
   thing of naught, third string, thug, tin, tinsel, titivated, token,
   tool, toy, travesty, trey, trick, trifle, trump, twisted,
   typesetting, typesetting machine, unauthentic, understudy,
   ungenuine, unnatural, unreal, utility, utility man, utility player,
   vehicle, version, vicar, vicar general, vicarious, vice,
   vice-president, vice-regent, vicegerent, votary, warped,
   wax figure, waxwork, whiffet, whippersnapper, whited sepulcher,
   witling, wood carving, wood model, yes-man, zero