chalk \chalk\ chaddk, 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.
      1913 webster

   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.
      1913 webster

   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.
      1913 webster
see also:
calz cawk crayon black chalk by a long chalk chalk drawing 
chalk formation cretaceous formation cretaceous chalk line chalk mixture 
chalk period cretaceous period chalk pit drawing chalk french chalk 
red chalk