The Collaborative International Dictionary of English v.0.48:

Sustain \Sus*tain"\, v. t. [imp. & p. p. Sustained; p. pr. &
   vb. n. Sustaining.] [OE. sustenen, susteinen, OF. sustenir,
   sostenir, F. soutenir (the French prefix is properly fr. L.
   subtus below, fr. sub under), L. sustinere; pref. sus- (see
   Sub-) + tenere to hold. See Tenable, and cf.
   Sustenance.]
   1. To keep from falling; to bear; to uphold; to support; as,
      a foundation sustains the superstructure; a beast sustains
      a load; a rope sustains a weight.
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            Every pillar the temple to sustain.   --Chaucer.
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   2. Hence, to keep from sinking, as in despondence, or the
      like; to support.
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            No comfortable expectations of another life to
            sustain him under the evils in this world.
                                                  --Tillotson.
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   3. To maintain; to keep alive; to support; to subsist; to
      nourish; as, provisions to sustain an army.
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   4. To aid, comfort, or relieve; to vindicate. --Shak.
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            His sons, who seek the tyrant to sustain. --Dryden.
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   5. To endure without failing or yielding; to bear up under;
      as, to sustain defeat and disappointment.
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   6. To suffer; to bear; to undergo.
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            Shall Turnus, then, such endless toil sustain?
                                                  --Dryden.
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            You shall sustain more new disgraces. --Shak.
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   7. To allow the prosecution of; to admit as valid; to
      sanction; to continue; not to dismiss or abate; as, the
      court sustained the action or suit.
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   8. To prove; to establish by evidence; to corroborate or
      confirm; to be conclusive of; as, to sustain a charge, an
      accusation, or a proposition.
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   Syn: To support; uphold; subsist; assist; relieve; suffer;
        undergo.
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The Collaborative International Dictionary of English v.0.48:

Sustained \Sus*tained"\, a.
   Held up to a certain pitch, degree, or level; uniform; as,
   sustained pasion; a sustained style of writing; a sustained
   note in music.
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WordNet (r) 3.0 (2006):

sustained
    adj 1: maintained at length without interruption or weakening;
           "sustained flight"
    2: (of an electric arc) continuous; "heat transfer to the anode
       in free burning arcs" [syn: free burning, sustained]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "sustained":
   abiding, based on, bolstered, borne, braced, buttressed, ceaseless,
   changeless, chattering, constant, continual, continued, continuing,
   continuous, durable, enduring, even, firm, fixed, founded on,
   frozen, grounded on, guyed, held, immobile, immutable, incessant,
   indefatigable, intact, interminable, inviolate, lasting, level,
   machine gun, maintained, oscillating, perennial, permanent,
   perpetual, persistent, prolonged, propped, pulsating, quiescent,
   rapid, regular, remaining, repeated, rigid, shored up, solid,
   stable, staccato, static, stationary, stayed, staying, steadfast,
   steady, sticking, stuttering, supported, torpid, unaltered,
   unbroken, unceasing, unchangeable, unchanged, unchanging,
   unchecked, undestroyed, undying, unfading, unfailing, uniform,
   unintermitted, unintermittent, unintermitting, uninterrupted,
   unremitting, unshifting, unstopped, unvaried, unvarying, upheld,
   vibrating