Source : Webster's Revised Unabridged Dictionary (1913)

Chalk \Chalk\, n. [AS. cealc lime, from L. calx limestone. See
   {Calz}, and {Cawk}.]
   1. (Min.) A soft, earthy substance, of a white, grayish, or
      yellowish white color, consisting of calcium carbonate,
      and having the same composition as common limestone.

   2. (Fine Arts) Finely prepared chalk, used as a drawing
      implement; also, by extension, a compound, as of clay and
      black lead, or the like, used in the same manner. See
      {Crayon}.

   {Black chalk}, a mineral of a bluish color, of a slaty
      texture, and soiling the fingers when handled; a variety
      of argillaceous slate.

   {By a long chalk}, by a long way; by many degrees. [Slang]
      --Lowell.

   {Chalk drawing} (Fine Arts), a drawing made with crayons. See
      {Crayon}.

   {Chalk formation}. See {Cretaceous formation}, under
      {Cretaceous}.

   {Chalk line}, a cord rubbed with chalk, used for making
      straight lines on boards or other material, as a guide in
      cutting or in arranging work.

   {Chalk mixture}, a preparation of chalk, cinnamon, and sugar
      in gum water, much used in diarrheal affection, esp. of
      infants.

   {Chalk period}. (Geol.) See {Cretaceous period}, under
      {Cretaceous}.

   {Chalk pit}, a pit in which chalk is dug.

   {Drawing chalk}. See {Crayon}, n., 1.

   {French chalk}, steatite or soapstone, a soft magnesian
      mineral.

   {Red chalk}, an indurated clayey ocher containing iron, and
      used by painters and artificers; reddle.

Source : WordNet®

chalk line
     n : a chalked string used in the building trades to make a
         straight line on a vertical surface [syn: {snap line}, {snapline}]