The Collaborative International Dictionary of English v.0.48:

Ash \Ash\, n.,
   sing. of Ashes.
   [1913 Webster]

   Note: Ash is rarely used in the singular except in connection
         with chemical or geological products; as, soda ash,
         coal which yields a red ash, etc., or as a qualifying
         or combining word; as, ash bin, ash heap, ash hole, ash
         pan, ash pit, ash-grey, ash-colored, pearlash, potash.
         [1913 Webster]

   Bone ash, burnt powered; bone earth.

   Volcanic ash. See under Ashes.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ashes \Ash"es\, n. pl. [OE. asche, aske, AS. asce, [ae]sce, axe;
   akin to OHG. asca, G. asche, D. asch, Icel. & Sw. aska, Dan.
   aske, Goth. azgo.]
   1. The earthy or mineral particles of combustible substances
      remaining after combustion, as of wood or coal.
      [1913 Webster]

   2. Specifically: The remains of the human body when burnt, or
      when "returned to dust" by natural decay.
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            Their martyred blood and ashes sow.   --Milton.
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            The coffins were broken open. The ashes were
            scattered to the winds.               --Macaulay.
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   3. The color of ashes; deathlike paleness.
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            The lip of ashes, and the cheek of flame. --Byron.
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   In dust and ashes, In sackcloth and ashes, with humble
      expression of grief or repentance; -- from the method of
      mourning in Eastern lands.

   Volcanic ashes, or Volcanic ash, the loose, earthy
      matter, or small fragments of stone or lava, ejected by
      volcanoes.
      [1913 Webster]