The Collaborative International Dictionary of English v.0.48:

Impress \Im"press\, n.; pl. Impresses.
   1. The act of impressing or making.
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   2. A mark made by pressure; an indentation; imprint; the
      image or figure of anything, formed by pressure or as if
      by pressure; result produced by pressure or influence.
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            The impresses of the insides of these shells.
                                                  --Woodward.
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            This weak impress of love is as a figure
            Trenched in ice.                      --Shak.
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   3. Characteristic; mark of distinction; stamp. --South.
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   4. A device. See Impresa. --Cussans.
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            To describe . . . emblazoned shields,
            Impresses quaint.                     --Milton.
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   5. [See Imprest, Press to force into service.] The act of
      impressing, or taking by force for the public service;
      compulsion to serve; also, that which is impressed.
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            Why such impress of shipwrights?      --Shak.
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   Impress gang, a party of men, with an officer, employed to
      impress seamen for ships of war; a press gang.

   Impress money, a sum of money paid, immediately upon their
      entering service, to men who have been impressed.
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The Collaborative International Dictionary of English v.0.48:

Press \Press\, n. [For prest, confused with press.]
   A commission to force men into public service, particularly
   into the navy.
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         I have misused the king's press.         --Shak.
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   Press gang, or Pressgang, a detachment of seamen under
      the command of an officer empowered to force men into the
      naval service. See Impress gang, under Impress.

   Press money, money paid to a man enlisted into public
      service. See Prest money, under Prest, a.
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WordNet (r) 3.0 (2006):

press gang
    n 1: a detachment empowered to force civilians to serve in the
         army or navy