An Etymological Dictionary of Astronomy and Astrophysics

A rotational or orbital movement that is the same as most
bodies within a celestial system. In the solar system, the apparent eastward motion of a celestial body on the celestial sphere. Opposed to → retrograde motion. Same as → direct motion.

Etymology (EN): From → pro- “forward” + grade, from L. gradi “to go, step, walk;” → motion.

Etymology (PE): Jonbeš, → motion; farârow, from farâ- “forward,” → pro-, + row present stem of raftan “to go, walk;” Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- “to go; to attack.”