The Collaborative International Dictionary of English v.0.48:

Inarticulate \In`ar*tic"u*late\, a. [L. inarticulatus; pref. in-
   not + articulatus articulate.]
   [1913 Webster]
   1. Not uttered with articulation or intelligible
      distinctness, as speech or words.
      [1913 Webster]

            Music which is inarticulate poesy.    --Dryden.
      [1913 Webster]

   2. (Zool.)
      (a) Not jointed or articulated; having no distinct body
          segments; as, an inarticulate worm.
      (b) Without a hinge; -- said of an order (Inarticulata
          or Ecardines) of brachiopods.
          [1913 Webster]

   3. Incapable of articulating. [R.]
      [1913 Webster]

            The poor earl, who is inarticulate with palsy.
                                                  --Walpole.

   4. Incapable of expressing one's ideas or feelings clearly.
      [PJC]

WordNet (r) 3.0 (2006):

inarticulate
    adj 1: without or deprived of the use of speech or words;
           "inarticulate beasts"; "remained stupidly inarticulate
           and saying something noncommittal"; "inarticulate with
           rage"; "an inarticulate cry" [syn: inarticulate,
           unarticulate] [ant: articulate]

Moby Thesaurus II by Grady Ward, 1.0:

102 Moby Thesaurus words for "inarticulate":
   Greek to one, ambiguous, anaudic, aphasic, aphonic, bashful,
   beyond understanding, blurred, breathless, breathy, choked,
   choking, confused, conscious, coy, croaking, demure, digressive,
   discursive, disjointed, drawling, drawly, dumb, dumbfounded,
   dumbstricken, dumbstruck, dysphonic, faltering, garbled, guttural,
   halting, harsh, hawking, hesitating, hoarse, illogical,
   impenetrable, implicit, implied, incognizable, incoherent,
   incomprehensible, indistinct, inferred, inscrutable, irrational,
   jumbled, lisping, maundering, mispronounced, mixed-up, mousy,
   muddled, muffled, mum, mumbled, mumbling, mute, muzzy, nasal,
   numinous, past comprehension, quavering, rambling, scrambled,
   self-conscious, shaking, shaky, shamefaced, shamefast, shy, silent,
   skittish, snuffling, speechless, stammering, stifled, strangled,
   stricken dumb, thick, throaty, timid, timorous, tongue-tied,
   tongueless, tremulous, twangy, unclear, unconnected, undeclared,
   unexpressed, unfathomable, unintelligible, unknowable, unsaid,
   unsearchable, unspoken, unuttered, velar, voiceless, wild,
   wordless