/ Dictionary / Index P planetary precession: Meaning and Definition of Find definitions for: plan'etary preces'sion Pronunciation: [key] — Astron. Astron. the small component of the precession of the equinoxes contributed by the motion of the ecliptic, the change in orientation of the plane of the earth's orbit being produced by the gravitational attraction of the planets. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. planetary nebula planetesimal Related Content Daily Word Quiz: immense Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language