radial motion

noun Astronomy.
  1. the component of the motion of a star away from or toward the earth along its line of sight, expressed in miles or kilometers per second and determined by the shift in the wavelength of light emitted by the star.
Also called radial velocity.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for radial velocity

radial velocity

noun
  1. the component of the velocity of an object, esp a celestial body, directed along a line from the observer to the object
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012