hodograph

from The Century Dictionary.

• noun A curve the radius vector of which represents in magnitude and direction the velocity of a moving particle. It was invented by Sir W. R. Hamilton.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.