The Collaborative International Dictionary of English v.0.48:

Muffler \Muf"fler\, n.
   1. Anything used in muffling; esp., a scarf for protecting
      the head and neck in cold weather; a tippet.
      [1913 Webster]

            Fortune is painted blind, with a muffler above her
            eyes.                                 --Shak.
      [1913 Webster]

   2. (Mus.) A cushion for terminating or softening a note made
      by a stringed instrument with a keyboard.
      [1913 Webster]

   3. A kind of mitten or boxing glove, esp. when stuffed.
      [1913 Webster]

   4. One who muffles.
      [1913 Webster]

   5. (Mach.) Any of various devices to deaden the noise of
      escaping gases or vapors, as a tube filled with
      obstructions, through which the exhaust gases of an
      internal-combustion engine, as on an automobile, are
      passed (called also silencer).
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

muffler
    n 1: a tubular acoustic device inserted in the exhaust system
         that is designed to reduce noise [syn: silencer,
         muffler]
    2: a scarf worn around the neck
    3: a device that decreases the amplitude of electronic,
       mechanical, acoustical, or aerodynamic oscillations [syn:
       damper, muffler]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "muffler":
   PCV valve, Roman collar, accelerator, acoustic tile, alternator,
   ammeter, antiknock, baffler, band, bandanna, bearings, bertha, boa,
   bonnet, boot, bowtie, brake, bucket seat, bumper,
   button-down collar, camshaft, carburetor, celluloid collar,
   chassis, choke, choker, clerical collar, cloak, clutch, collar,
   comforter, connecting rod, convertible top, cover, cowl, crank,
   crankcase, crankshaft, cravat, cushion, cutout, cylinder,
   cylinder head, damp, dampener, damper, dash, dashboard,
   differential, disguise, distributor, dog collar, exhaust,
   exhaust pipe, facade, fan, fender, flywheel, four-in-hand, fur,
   gag, gear, gearbox, gearshift, generator, guimpe, guise, headlight,
   headrest, hood, horn, hushcloth, ignition, intake, kerchief,
   manifold, masquerade, muffle, mute, muzzle, neckband, neckcloth,
   neckerchief, neckpiece, necktie, parking light, piston,
   plunging neckline, power brakes, power steering, quietener,
   radiator, rear-view mirror, ruff, scarf, seat belt, shawl,
   shock absorber, silence cloth, silencer, soft pedal, sordine,
   sordino, sound-absorbing material, soundproofing,
   soundproofing insulation, sourdine, spark plug, speedometer,
   springs, starter, steering wheel, stock, stole, tallith, tie,
   tippet, top, transmission, tucker, universal, valve, veil, veneer,
   windscreen, windshield, wrap