Chalk  —n. 1 white soft limestone. 2 a similar substance, sometimes coloured, for writing or drawing. B piece of this. —v. 1 rub, mark, draw, or write with chalk. 2 (foll. By up) a write or record with chalk. B register or gain (success etc.).  by a long chalk by far.  chalky adj. (-ier, -iest). Chalkiness n. [latin *calx]