—pl.radii vec•to•resPronunciation: (vek-tôr'ēz, -tōr'-),[key]radius vectors. 1. Math.the length of the line segment joining a fixed point or origin to a given point.
2. Astron. a. the straight line joining two bodies in relative orbital motion, as the line from the sun to a planet at any point in its orbit.
b. the distance between two such bodies at any point in the orbit.