noun
( plural radii vecto·res -ˌvekˈtōr(ˌ)ēz)
1. : a straight line segment or its length from a fixed point, pole, or center to a variable point : the linear polar coordinate of a variable point
2. : a straight line joining the center of an attracting body (as the sun) with that of a body (as a planet or comet) describing an orbit around it