The Collaborative International Dictionary of English v.0.48:

Muddy \Mud"dy\, a. [Compar. Muddier; superl. Muddiest.]
   1. Abounding in mud; besmeared or dashed with mud; as, a
      muddy road or path; muddy boots.
      [1913 Webster]

   2. Turbid with mud; as, muddy water.
      [1913 Webster]

   3. Consisting of mud or earth; gross; impure.
      [1913 Webster]

            This muddy vesture of decay.          --Shak.
      [1913 Webster]

   4. Confused, as if turbid with mud; cloudy in mind; dull;
      stupid; also, immethodical; incoherent; vague.
      [1913 Webster]

            Cold hearts and muddy understandings. --Burke.
      [1913 Webster]

            Dost think I am so muddy, so unsettled. --Shak.
      [1913 Webster]

   5. Not clear or bright. --Swift.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Muddy \Mud"dy\, v. t. [imp. & p. p. Muddied; p. pr. & vb. n.
   Muddying.]
   1. To soil with mud; to dirty; to render turbid.
      [1913 Webster]

   2. (Fig.): To cloud; to make dull or heavy; to confuse.
      --Grew.
      [1913 Webster]

WordNet (r) 3.0 (2006):

muddy
    adj 1: (of soil) soft and watery; "the ground was boggy under
           foot"; "a marshy coastline"; "miry roads"; "wet mucky
           lowland"; "muddy barnyard"; "quaggy terrain"; "the
           sloughy edge of the pond"; "swampy bayous" [syn: boggy,
           marshy, miry, mucky, muddy, quaggy, sloppy,
           sloughy, soggy, squashy, swampy, waterlogged]
    2: dirty and messy; covered with mud or muck; "muddy boots"; "a
       mucky stable" [syn: mucky, muddy]
    3: (of color) discolored by impurities; not bright and clear;
       "dirty" is often used in combination; "a dirty (or dingy)
       white"; "the muddied grey of the sea"; "muddy colors";
       "dirty-green walls"; "dirty-blonde hair" [syn: dirty,
       dingy, muddied, muddy]
    4: (of liquids) clouded as with sediment; "a cloudy liquid";
       "muddy coffee"; "murky waters" [syn: cloudy, muddy,
       mirky, murky, turbid]
    v 1: dirty with mud [syn: muddy, muddy up]
    2: cause to become muddy; "These data would have muddied the
       prediction"
    3: make turbid; "muddy the water"

Moby Thesaurus II by Grady Ward, 1.0:

207 Moby Thesaurus words for "muddy":
   achromatic, achromic, addled, amorphous, anemic, ashen, ashy,
   becloud, bedraggled, befog, befouled, begrime, bemire, bemud,
   besmirch, besmirched, besmoke, besoil, bespatter, black,
   bled white, blind, bloodless, blotchy, blur, blurred, boggish,
   boggy, cadaverous, chloranemic, chuckhole, clear as mud, cloud,
   cloudy, colorless, conceal, confuse, confused, dark, dead,
   deadly pale, deathly pale, dim, dimmed, dingy, dirt, dirty,
   dirty up, discolored, drab, draggled, dull, dungy, dust, dusty,
   etiolated, exsanguinated, exsanguine, exsanguineous, fade, faded,
   faint, fallow, feculent, fenny, filthy, flat, fog, foggy, foul,
   fouled, fuliginous, fuzz, fuzzy, ghastly, gloomy, gray, grime,
   grimy, grubby, grungy, haggard, hazy, hick town, hide, hueless,
   hypochromic, impure, indeterminate, indistinct, jerkwater town,
   lackluster, leaden, livid, lurid, lusterless, make uncertain,
   marish, marshy, mat, mealy, messy, mire, mirish, miry, misty,
   mix up, mixed-up, moorish, moory, muck, muck up, mucky, mud,
   muddle, muddled, mudhole, murky, nasty, nebulous, neutral, obscure,
   one-horse town, oozy, opaque, pale, pale as death, pale-faced,
   pallid, paludal, paludous, pasty, plashy, poachy, quaggy, quagmiry,
   rile, riley, roily, sallow, screen, scruffy, shadowy, shapeless,
   sickly, slabby, slime, slimy, slobby, sloppy, sloshy, sloughy,
   slovenly, sludgy, slushy, smirch, smirched, smirchy, smoke, smoky,
   smooch, smudge, smudgy, smutchy, smutty, snuffy, soft, soil,
   soiled, soily, soot, sooty, sordid, spatter, splashy, sposhy,
   spouty, squalid, squashy, squelchy, squishy, squushy, subdued,
   subfusc, swampish, swampy, tallow-faced, tarnish, toneless,
   transcendent, turbid, uliginous, unclean, uncleanly, unclear,
   uncolored, unplain, untidy, vague, wan, washed out, washed-out,
   waxen, weak, whey-faced, whistle-stop, white



U.S. Gazetteer Places (2000):

Muddy, MT -- U.S. Census Designated Place in Montana
   Population (2000):    627
   Housing Units (2000): 160
   Land area (2000):     28.561963 sq. miles (73.975142 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    28.561963 sq. miles (73.975142 sq. km)
   FIPS code:            52315
   Located within:       Montana (MT), FIPS 30
   Location:             45.599225 N, 106.739578 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Muddy, MT
    Muddy


U.S. Gazetteer Places (2000):

Muddy, IL -- U.S. village in Illinois
   Population (2000):    78
   Housing Units (2000): 39
   Land area (2000):     0.262714 sq. miles (0.680427 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.262714 sq. miles (0.680427 sq. km)
   FIPS code:            51271
   Located within:       Illinois (IL), FIPS 17
   Location:             37.764086 N, 88.514469 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Muddy, IL
    Muddy