The Collaborative International Dictionary of English v.0.48:

Indefinite \In*def"i*nite\, a. [L. indefinitus. See In- not,
   and Definite.]
   [1913 Webster]
   1. Not definite; not limited, defined, or specified; not
      explicit; not determined or fixed upon; not precise;
      uncertain; vague; confused; obscure; as, an indefinite
      time, plan, etc.
      [1913 Webster]

            It were to be wished that . . . men would leave off
            that indefinite way of vouching, "the chymists say
            this," or "the chymists affirm that." --Boyle.
      [1913 Webster]

            The time of this last is left indefinite. --Dryden.
      [1913 Webster]

   2. Having no determined or certain limits; large and
      unmeasured, though not infinite; unlimited; as, indefinite
      space; the indefinite extension of a straight line.
      [1913 Webster]

            Though it is not infinite, it may be indefinite;
            though it is not boundless in itself, it may be so
            to human comprehension.               --Spectator.
      [1913 Webster]

   3. Boundless; infinite. [R.]
      [1913 Webster]

            Indefinite and omnipresent God,
            Inhabiting eternity.                  --W. Thompson
                                                  (1745).
      [1913 Webster]

   4. (Bot.) Too numerous or variable to make a particular
      enumeration important; -- said of the parts of a flower,
      and the like. Also, indeterminate.
      [1913 Webster]

   Indefinite article (Gram.), the word a or an, used with
      nouns to denote any one of a common or general class.

   Indefinite inflorescence. (Bot.) See Indeterminate
      inflorescence, under Indeterminate.

   Indefinite proposition (Logic), a statement whose subject
      is a common term, with nothing to indicate distribution or
      nondistribution; as, Man is mortal.

   Indefinite term (Logic), a negative term; as, the not-good.

   Syn: Inexplicit; vague; uncertain; unsettled; indeterminate;
        loose; equivocal; inexact; approximate.
        [1913 Webster]

WordNet (r) 3.0 (2006):

indefinite
    adj 1: vague or not clearly defined or stated; "must you be so
           indefinite?"; "amorphous blots of color having vague and
           indefinite edges"; "he would not answer so indefinite a
           proposal" [ant: definite]
    2: not decided or not known; "were indefinite about their
       plans"; "plans are indefinite"

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "indefinite":
   abstract, aleatoric, aleatory, ambiguous, amorphic, amorphous,
   anarchic, baffling, baggy, bewildering, bland, blear, bleared,
   bleary, blobby, blurred, blurry, boundless, broad, chance, chancy,
   chaotic, characterless, collective, confused, confusing, cryptic,
   dark, dim, disordered, disorderly, endless, enduring, equivocal,
   faint, featureless, feeble, filmy, foggy, formless, fuzzy, general,
   generalized, generic, half-seen, half-visible, hazy, hesitant,
   hit-or-miss, ill-defined, immeasurable, imprecise, inaccurate,
   incalculable, inchoate, incoherent, inconspicuous, inconstant,
   indecisive, indefinable, indelible, indestructible, indeterminable,
   indeterminate, indistinct, indistinguishable, ineffaceable,
   ineradicable, inexact, inexplicit, infinite, inform, kaleidoscopic,
   lax, limitless, loose, low-profile, lumpen, measureless,
   merely glimpsed, misty, mystifying, nebulous, neutral, nondescript,
   nonspecific, obscure, orderless, out of focus, pale, permanent,
   puzzling, random, semivisible, shadowed forth, shadowy, shapeless,
   shilly-shallying, stochastic, sub judice, sweeping, unbounded,
   uncertain, uncharacterized, unclear, uncountable, uncounted,
   undecided, undefinable, undefined, undestined, undestroyable,
   undetermined, undifferentiated, unerasable, unfixed, unknown,
   unlimited, unmeasured, unordered, unorganized, unplain,
   unrecognizable, unsettled, unspecific, unspecified, unsure,
   vacillating, vague, veiled, wavering, weak, wide, wishy-washy



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

INDEFINITE. That which is undefined; uncertain.



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

INDEFINITE, NUMBER. A number which may be increased or diminished at
pleasure.
     2. When a corporation is composed of an indefinite number of persons,
any number of them consisting of a majority of those present may do any act
unless it be otherwise regulated by the charter or by-laws. See Definite
number.