The Collaborative International Dictionary of English v.0.48:

Chalk \Chalk\ (ch[add]k), 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]

The Collaborative International Dictionary of English v.0.48:

chalk line \chalk" line`\ (ch[add]k" l[imac]n`), n.
   1. a string impregnated with powdered chalk, used in
      construction to mark a straight line on a surface, such as
      a wall. The string is held taut on the surface between the
      two end points of the line to be made, the center of the
      line is drawn away from the surface, and the string is
      released and snapped against the surface, leaving a line
      of chalk in the desired location.
      [PJC]

   2. the line of chalk on a surface left by a chalk line[1].
      [PJC]

WordNet (r) 3.0 (2006):

chalk line
    n 1: a chalked string used in the building trades to make a
         straight line on a vertical surface [syn: chalk line,
         snap line, snapline]