The Collaborative International Dictionary of English v.0.48:

Porcelain \Por"ce*lain\ (277), n. [F. porcelaine, It.
   porcellana, orig., the porcelain shell, or Venus shell
   (Cypr[ae]a porcellana), from a dim. fr. L. porcus pig,
   probably from the resemblance of the shell in shape to a
   pig's back. Porcelain was called after this shell, either on
   account of its smoothness and whiteness, or because it was
   believed to be made from it. See Pork.]
   A fine translucent or semitransculent kind of earthenware,
   made first in China and Japan, but now also in Europe and
   America; -- called also China, or China ware.
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         Porcelain, by being pure, is apt to break. --Dryden.
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   Ivory porcelain, porcelain with a surface like ivory,
      produced by depolishing. See Depolishing.

   Porcelain clay. See under Clay.

   Porcelain crab (Zool.), any crab of the genus Porcellana
      and allied genera (family Porcellanid[ae]). They have a
      smooth, polished carapace.

   Porcelain jasper. (Min.) See Porcelanite.

   Porcelain printing, the transferring of an impression of an
      engraving to porcelain.

   Porcelain shell (Zool.), a cowry.
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The Collaborative International Dictionary of English v.0.48:

Clay \Clay\ (kl[=a]), n. [AS. cl[=ae]g; akin to LG. klei, D.
   klei, and perh. to AS. cl[=a]m clay, L. glus, gluten glue,
   Gr. gloio`s glutinous substance, E. glue. Cf. Clog.]
   1. A soft earth, which is plastic, or may be molded with the
      hands, consisting of hydrous silicate of aluminium. It is
      the result of the wearing down and decomposition, in part,
      of rocks containing aluminous minerals, as granite. Lime,
      magnesia, oxide of iron, and other ingredients, are often
      present as impurities.
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   2. (Poetry & Script.) Earth in general, as representing the
      elementary particles of the human body; hence, the human
      body as formed from such particles.
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            I also am formed out of the clay.     --Job xxxiii.
                                                  6.
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            The earth is covered thick with other clay,
            Which her own clay shall cover.       --Byron.
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   Bowlder clay. See under Bowlder.

   Brick clay, the common clay, containing some iron, and
      therefore turning red when burned.

   Clay cold, cold as clay or earth; lifeless; inanimate.

   Clay ironstone, an ore of iron consisting of the oxide or
      carbonate of iron mixed with clay or sand.

   Clay marl, a whitish, smooth, chalky clay.

   Clay mill, a mill for mixing and tempering clay; a pug
      mill.

   Clay pit, a pit where clay is dug.

   Clay slate (Min.), argillaceous schist; argillite.

   Fatty clays, clays having a greasy feel; they are chemical
      compounds of water, silica, and aluminia, as halloysite,
      bole, etc.

   Fire clay, a variety of clay, entirely free from lime,
      iron, or an alkali, and therefore infusible, and used for
      fire brick.

   Porcelain clay, a very pure variety, formed directly from
      the decomposition of feldspar, and often called kaolin.


   Potter's clay, a tolerably pure kind, free from iron.
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WordNet (r) 3.0 (2006):

porcelain clay
    n 1: a fine usually white clay formed by the weathering of
         aluminous minerals (as feldspar); used in ceramics and as
         an absorbent and as a filler (e.g., in paper) [syn: china
         clay, china stone, kaolin, kaoline, porcelain
         clay, terra alba]