The Collaborative International Dictionary of English v.0.48:

Stamp \Stamp\, n.
   1. The act of stamping, as with the foot.
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   2. The which stamps; any instrument for making impressions on
      other bodies, as a die.
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            'T is gold so pure
            It can not bear the stamp without alloy. --Dryden.
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   3. The mark made by stamping; a mark imprinted; an
      impression.
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            That sacred name gives ornament and grace,
            And, like his stamp, makes basest metals pass.
                                                  --Dryden.
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   4. That which is marked; a thing stamped.
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            Hanging a golden stamp about their necks. --Shak.
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   5. [F. estampe, of German origin. See Stamp, v. t.] A
      picture cut in wood or metal, or made by impression; a
      cut; a plate. [Obs.]
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            At Venice they put out very curious stamps of the
            several edifices which are most famous for their
            beauty and magnificence.              --Addison.
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   6. An official mark set upon things chargeable with a duty or
      tax to government, as evidence that the duty or tax is
      paid; as, the stamp on a bill of exchange.
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   7. Hence: A stamped or printed device, usually paper, issued
      by the government at a fixed price, and required by law to
      be affixed to, or stamped on, certain papers, as evidence
      that the government dues are paid; as, a postage stamp; a
      tax stamp; a receipt stamp, etc.
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   8. An instrument for cutting out, or shaping, materials, as
      paper, leather, etc., by a downward pressure.
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   9. A character or reputation, good or bad, fixed on anything
      as if by an imprinted mark; current value; authority; as,
      these persons have the stamp of dishonesty; the Scriptures
      bear the stamp of a divine origin.
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            Of the same stamp is that which is obtruded on us,
            that an adamant suspends the attraction of the
            loadstone.                            --Sir T.
                                                  Browne.
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   10. Make; cast; form; character; as, a man of the same stamp,
       or of a different stamp.
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             A soldier of this season's stamp.    --Shak.
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   11. A kind of heavy hammer, or pestle, raised by water or
       steam power, for beating ores to powder; anything like a
       pestle, used for pounding or beating.
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   12. A half-penny. [Obs.] --Beau. & Fl.
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   13. pl. Money, esp. paper money. [Slang, U.S.]
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   Stamp act, an act of the British Parliament [1765] imposing
      a duty on all paper, vellum, and parchment used in the
      American colonies, and declaring all writings on unstamped
      materials to be null and void.

   Stamp collector,
       (a) an officer who receives or collects stamp duties.
       (b) one who collects postage or other stamps, as an
           avocation or for investment; a philatelist.

   Stamp duty, a duty, or tax, imposed on paper and parchment
      used for certain writings, as deeds, conveyances, etc.,
      the evidence of the payment of the duty or tax being a
      stamp. [Eng.]

   Stamp hammer, a hammer, worked by power, which rises and
      falls vertically, like a stamp in a stamp mill.

   Stamp head, a heavy mass of metal, forming the head or
      lower end of a bar, which is lifted and let fall, in a
      stamp mill.

   Stamp mill (Mining), a mill in which ore is crushed with
      stamps; also, a machine for stamping ore.

   Stamp note, a stamped certificate from a customhouse
      officer, which allows goods to be received by the captain
      of a ship as freight. [Eng.]

   Stamp office, an office for the issue of stamps and the
      reception of stamp duties.
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WordNet (r) 3.0 (2006):

Stamp Act
    n 1: an act passed by the British Parliament in 1756 that raised
         revenue from the American Colonies by a duty in the form of
         a stamp required on all newspapers and legal or commercial
         documents; opposition by the Colonies resulted in the
         repeal of the act in 1766