Source : Webster's Revised Unabridged Dictionary (1913)

Hodograph \Hod"o*graph\, n. [Gr.? path + graph.] (Math.)
   A curve described by the moving extremity of a line the other
   end of which is fixed, this line being constantly parallel to
   the direction of motion of, and having its length constantly
   proportional to the velocity of, a point moving in any path;
   -used in investigations respecting central forces.