The Collaborative International Dictionary of English v.0.48:

Siege \Siege\, n. [OE. sege, OF. siege, F. si[`e]ge a seat, a
   siege; cf. It. seggia, seggio, zedio, a seat, asseggio,
   assedio, a siege, F. assi['e]ger to besiege, It. & LL.
   assediare, L. obsidium a siege, besieging; all ultimately fr.
   L. sedere to sit. See Sit, and cf. See, n.]
   1. A seat; especially, a royal seat; a throne. [Obs.] "Upon
      the very siege of justice." --Shak.
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            A stately siege of sovereign majesty,
            And thereon sat a woman gorgeous gay. --Spenser.
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            In our great hall there stood a vacant chair . . .
            And Merlin called it "The siege perilous."
                                                  --Tennyson.
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   2. Hence, place or situation; seat. [Obs.]
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            Ah! traitorous eyes, come out of your shameless
            siege forever.                        --Painter
                                                  (Palace of
                                                  Pleasure).
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   3. Rank; grade; station; estimation. [Obs.]
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            I fetch my life and being
            From men of royal siege.              --Shak.
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   4. Passage of excrements; stool; fecal matter. [Obs.]
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            The siege of this mooncalf.           --Shak.
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   5. The sitting of an army around or before a fortified place
      for the purpose of compelling the garrison to surrender;
      the surrounding or investing of a place by an army, and
      approaching it by passages and advanced works, which cover
      the besiegers from the enemy's fire. See the Note under
      Blockade.
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   6. Hence, a continued attempt to gain possession.
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            Love stood the siege, and would not yield his
            breast.                               --Dryden.
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   7. The floor of a glass-furnace.
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   8. A workman's bench. --Knught.
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   Siege gun, a heavy gun for siege operations.

   Siege train, artillery adapted for attacking fortified
      places.
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The Collaborative International Dictionary of English v.0.48:

Siege \Siege\, v. t.
   To besiege; to beset. [R.]
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         Through all the dangers that can siege
         The life of man.                         --Buron.
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WordNet (r) 3.0 (2006):

siege
    n 1: the action of an armed force that surrounds a fortified
         place and isolates it while continuing to attack [syn:
         siege, besieging, beleaguering, military blockade]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "siege":
   attack, beleaguer, beleaguerment, besetment, besiege, besiegement,
   blockade, blockading, bottle up, bout, circumscription,
   confinement, cordon off, cordoning, encircle, encirclement,
   enclosure, encompassment, envelopment, go, immurement,
   imprisonment, incarceration, inclusion, investment, lay siege to,
   onslaught, pincer movement, quarantine, seizure, spell,
   vertical envelopment