The Collaborative International Dictionary of English v.0.48:

Gradient \Gra"di*ent\, n.
   1. The rate of regular or graded ascent or descent in a road;
      grade.
      [1913 Webster]

   2. A part of a road which slopes upward or downward; a
      portion of a way not level; a grade.
      [1913 Webster]

   3. The rate of increase or decrease of a variable magnitude,
      or the curve which represents it; as, a thermometric
      gradient.

   4. (Chem., Biochem.) The variation of the concentration of a
      chemical substance in solution through some linear path;
      also called concentration gradient; -- usually measured in
      concentration units per unit distance. Concentration
      gradients are created naturally, e.g. by the diffusion of
      a substance from a point of high concentration toward
      regions of lower concentration within a body of liquid; in
      laboratory techniques they may be made artificially.
      [PJC]

   gradient maker (Biochem.) a device which creates a
      concentration gradient in a solution within some
      apparatus; -- used, e. g., for separation of biochemical
      substances.
      [PJC]

   Gradient post, a post or stake indicating by its height or
      by marks on it the grade of a railroad, highway, or
      embankment, etc., at that spot. Gradin