The Collaborative International Dictionary of English v.0.48:

Scrap \Scrap\ (skr[a^]p), n. [OE. scrappe, fr. Icel. skrap
   trifle, cracking. See Scrape, v. t.]
   1. Something scraped off; hence, a small piece; a bit; a
      fragment; a detached, incomplete portion.
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            I have no materials -- not a scrap.   --De Quincey.
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   2. Specifically, a fragment of something written or printed;
      a brief excerpt; an unconnected extract.
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   3. pl. The crisp substance that remains after drying out
      animal fat; as, pork scraps.
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   4. pl. Same as Scrap iron, below.
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   Scrap forgings, forgings made from wrought iron scrap.

   Scrap iron.
      (a) Cuttings and waste pieces of wrought iron from which
          bar iron or forgings can be made; -- called also
          wrought-iron scrap.
      (b) Fragments of cast iron or defective castings suitable
          for remelting in the foundry; -- called also foundry
          scrap, or cast scrap.
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WordNet (r) 3.0 (2006):

scrap iron
    n 1: iron to be melted again and reworked

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "scrap iron":
   bones, chaff, culm, deadwood, dishwater, draff, dregs, dust,
   filings, garbage, gash, hogwash, husks, leavings, lees, offal,
   offscourings, orts, parings, potsherds, rags, raspings, refuse,
   scourings, scraps, scum, shards, shavings, slack, slag, slop,
   slops, stubble, sweepings, swill, tares, wastage, waste,
   waste matter, wastepaper, weeds