The Collaborative International Dictionary of English v.0.48:

Vagueness \Vague"ness\, n.
   The quality or state of being vague.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vagueness
    n 1: unclearness by virtue of being poorly expressed or not
         coherent in meaning; "the Conservative manifesto is a model
         of vagueness"; "these terms were used with a vagueness that
         suggested little or no thought about what each might
         convey"
    2: indistinctness of shape or character; "the scene had the
       swirling vagueness of a painting by Turner"

Moby Thesaurus II by Grady Ward, 1.0:

110 Moby Thesaurus words for "vagueness":
   airiness, airy texture, amorphia, amorphism, amorphousness,
   anarchy, attenuation, bleariness, blobbiness, blur, blurriness,
   bodilessness, broadness, chaos, confusion, dark, darkness, defocus,
   delicacy, diaphanousness, dilutedness, dilution, dimness, disorder,
   entropy, ethereality, exiguity, exility, faintness, feebleness,
   filminess, fineness, flimsiness, fog, fogginess, formlessness,
   frailty, fuzziness, gauziness, generality, gossameriness,
   gracility, half-visibility, haziness, ill-definedness,
   immateriality, impalpability, imponderability, imprecision,
   inaccuracy, inchoateness, incoherence, incorporeality,
   indecisiveness, indefinableness, indefiniteness, indeterminateness,
   indistinctness, indistinguishability, inexactness,
   insubstantiality, intangibility, laciness, laxity, lightness,
   looseness, low profile, messiness, mist, mistiness, mumbo jumbo,
   murk, murkiness, mystification, obfuscation, obscurantism,
   obscuration, obscurity, opacity, orderlessness, paleness,
   paperiness, perplexity, rarity, semivisibility, shadowiness,
   shapelessness, slenderness, slightness, slimness, soft focus,
   subtility, subtlety, sweepingness, tenuity, tenuousness, thinness,
   uncertainty, unclarity, unclearness, unconcreteness, unplainness,
   unreality, unsolidity, unsubstantiality, unsubstantialness,
   vague appearance, wateriness, weakness, wispiness



Bouvier's Law Dictionary, Revised 6th Ed (1856):

VAGUENESS. Uncertainty.
     2. Certainty is required in contracts, wills, pleadings, judgments, and
indeed in all the acts on which courts have to give a judgment, and if they
be vague, so as not to be understood, they are in general invalid. 5 B. & C.
583; 1 Russ. & M. 116 1 Ch. Pract. 123. A charge of "frequent intemperance"
and "habitual indolence" are vague and too general. 2 Mart. Lo. Rep. N. S.
530. See Certainty; Nonsense; Uncertainty.