The Collaborative International Dictionary of English v.0.48:

Thousand \Thou"sand\, n. [OE. [thorn]ousend, [thorn]usend, AS.
   [thorn][=u]send; akin to OS. th[=u]sundig, th[=u]sind,
   OFries. thusend, D. duizend, G. tausend, OHG. t[=u]sunt,
   d[=u]sunt, Icel. [thorn][=u]sund, [thorn][=u]shund, Sw.
   tusen, Dan. tusind, Goth. [thorn][=u]sundi, Lith. tukstantis,
   Russ. tuisiacha; of uncertain origin.]
   1. The number of ten hundred; a collection or sum consisting
      of ten times one hundred units or objects.
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   2. Hence, indefinitely, a great number.
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            A thousand shall fall at thy side, and ten thousand
            at thy right hand.                    --Ps. xci. 7.
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   Note: The word thousand often takes a plural form. See the
         Note under Hundred.
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   3. A symbol representing one thousand units; as, 1,000, M or
      CI[Crev].
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The Collaborative International Dictionary of English v.0.48:

Thousand \Thou"sand\, a.
   1. Consisting of ten hundred; being ten times one hundred.
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   2. Hence, consisting of a great number indefinitely.
      "Perplexed with a thousand cares." --Shak.
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WordNet (r) 3.0 (2006):

thousand
    adj 1: denoting a quantity consisting of 1,000 items or units
           [syn: thousand, one thousand, 1000, m, k]
    n 1: the cardinal number that is the product of 10 and 100 [syn:
         thousand, one thousand, 1000, M, K, chiliad,
         G, grand, thou, yard]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "thousand":
   G, M, a billion, a crore, a lakh, a million, a myriad, a nonillion,
   a quadrillion, a thousand, a zillion, billion, chiliad, chiliagon,
   chiliahedron, chiliarch, chiliarchia, considerable, ever so many,
   full many, gobs, grand, heap, heaped-up, jillion, kilo, kilocycle,
   kilogram, kilohertz, kiloliter, kilometer, lakh, loads, many,
   millennium, millepede, milligram, milliliter, million,
   multifarious, multifold, multiple, multitudinal, multitudinous,
   myriad, no few, not a few, numerous, one hundred thousand, oodles,
   quantities, quite some, ten thousand, thou, trillion, very many,
   yard, zillion