The Collaborative International Dictionary of English v.0.48:

Murk \Murk\, a. [See Murky.]
   Dark; murky.
   [1913 Webster]

         He can not see through the mantle murk.  --J. R. Drake.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Murk \Murk\, n.
   Darkness; mirk. [Archaic] --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Murk \Murk\, n.
   The refuse of fruit, after the juice has been expressed;
   marc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

murk
    n 1: an atmosphere in which visibility is reduced because of a
         cloud of some substance [syn: fog, fogginess, murk,
         murkiness]
    v 1: make dark, dim, or gloomy

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "murk":
   amorphousness, bad light, becloud, bedarken, bedim, begloom,
   begrime, besmirch, besoil, black, black out, blacken, blackwash,
   block the light, blot, blot out, blotch, brown, cast a shadow,
   charcoal, cloud, cloud over, cork, dark, darken, darken over,
   darkishness, darkness, darksomeness, deadness, denigrate, dim,
   dim light, dim out, dimness, dinge, dirty, drabness, dullness,
   dusk, duskiness, duskness, ebonize, eclipse, encloud,
   encompass with shadow, flatness, fog, fogginess, foul, fuzziness,
   gloaming, gloom, grime, half-light, haze, indeterminateness,
   indistinctness, ink, lack of sparkle, lackluster, lifelessness,
   lusterlessness, mat, mat finish, melanize, mist, mistiness, muddy,
   mumbo jumbo, murkiness, mystification, nigrify, obfuscate,
   obfuscation, obnubilate, obscurantism, obscuration, obscure,
   obscurity, obumbrate, occult, occultate, opacity, overcast,
   overcloud, overshadow, oversmoke, partial darkness, perplexity,
   semidark, shade, shadow, shapelessness, smirch, smoke, smudge,
   smut, smutch, somber, somberness, soot, tarnish, twilight,
   unclarity, unclearness, unplainness, vagueness