D defs.my
Entry 2 senses Webster, 1913

Radius vector

/(vĕk"tŏr)/ · Ra·di·us vec·tor · IPA
01 n. A straight line (or the length of such line) connecting any point, as of a curve, with a fixed point, or pole, round which the straight lin…
  1. 1.
    A straight line (or the length of such line) connecting any point, as of a curve, with a fixed point, or pole, round which the straight line turns, and to which it serves to refer the successive points of a curve, in a system of polar coordinates. See Coordinate, n.(Math.) See: Coordinate
  2. 2.
    An ideal straight line joining the center of an attracting body with that of a body describing an orbit around it, as a line joining the sun and a planet or comet, or a planet and its satellite.(Astron.)