The Collaborative International Dictionary of English v.0.48:

Indistinct \In`dis*tinct"\ ([i^]n`d[i^]s*t[i^][ng]kt"), a. [L.
   indistinctus: cf. F. indistinct. See In- not, and
   Distinct.]
   [1913 Webster]
   1. Not distinct or distinguishable; not separate in such a
      manner as to be perceptible by itself; as, the indistinct
      parts of a substance. "Indistinct as water is in water."
      --Shak.
      [1913 Webster]

   2. Obscure to the mind or senses; not clear; not definite;
      confused; imperfect; faint; as, indistinct vision; an
      indistinct sound; an indistinct idea or recollection.
      [1913 Webster]

            When we come to parts too small four our senses, our
            ideas of these little bodies become obscure and
            indistinct.                           --I. Watts.
      [1913 Webster]

            Their views, indeed, are indistinct and dim.
                                                  --Cowper.

   Syn: Undefined; indistinguishable; obscure; indefinite;
        vague; ambiguous; uncertain; confused.
        [1913 Webster]

WordNet (r) 3.0 (2006):

indistinct
    adj 1: not clearly defined or easy to perceive or understand;
           "indistinct shapes in the gloom"; "an indistinct memory";
           "only indistinct notions of what to do" [ant: distinct]

Moby Thesaurus II by Grady Ward, 1.0:

139 Moby Thesaurus words for "indistinct":
   aleatoric, aleatory, alike, ambiguous, amorphous, barely audible,
   blear, bleared, bleary, blind, blobby, blurred, blurry, breathy,
   broad, chance, chancy, chaotic, choked, choking, clear as mud,
   cloudy, confused, croaking, dark, decrescendo, dim, disordered,
   distant, drawling, drawly, dysphonic, equivocal, faint,
   faint-voiced, feeble, filmy, foggy, fuzzy, general, gentle,
   guttural, half-heard, half-seen, half-visible, harsh, hawking,
   hazy, hit-or-miss, hoarse, ill-defined, illegible, imprecise,
   inaccurate, inarticulate, inchoate, incoherent, inconspicuous,
   indecisive, indefinable, indefinite, indeterminable, indeterminate,
   indiscernible, indistinctive, indistinguishable, inexact,
   inseparable, interchangeable, lax, lisping, loose, low,
   low-profile, merely glimpsed, mispronounced, misty, muddy, muffled,
   murky, murmured, muzzy, nasal, nebulous, nonspecific, obscure,
   opaque, orderless, out of focus, pale, pianissimo, piano,
   quavering, random, scarcely heard, semivisible, shadowed forth,
   shadowy, shaking, shaky, shapeless, snuffling, soft, soft-sounding,
   soft-voiced, standard, stereotyped, stifled, stochastic, strangled,
   subaudible, subdued, sweeping, thick, throaty, transcendent,
   tremulous, twangy, uncertain, unclear, undefined, undestined,
   undetermined, undifferentiated, undiscriminated, undistinguishable,
   undistinguished, uniform, unintelligible, unplain, unrecognizable,
   unspecified, vague, veiled, velar, weak, weak-voiced, whispered,
   without distinction