precession : Idioms & Phrases

• (Astron.), that portion of the annual precession of the equinoxes which depends on the joint action of the sun and moon.

Webster 1913

• that part of the precession of the equinoxes which depends on the action of the planets alone.

Webster 1913

• noun a slow westward shift of the equinoxes along the plane of the ecliptic caused by precession of the Earth's axis of rotation
  

WordNet

• (Astron.), the slow backward motion of the equinoctial points along the ecliptic, at the rate of 50.2&sec; annually, caused by the action of the sun, moon, and planets, upon the protuberant matter about the earth's equator, in connection with its diurnal rotation; so called because either equinox, owing to its westerly motion, comes to the meridian sooner each day than the point it would have occupied without the motion of precession, and thus precedes that point continually with reference to the time of transit and motion.

Webster 1913