/ Dictionary / Index I inner planet: Meaning and Definition of Find definitions for: in'ner plan'et Pronunciation: [key] — Astron. Astron. any of the four planets closest to the sun: Mercury, Venus, the earth, or Mars. Also calledCf. outer planet. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. innermost inner product Related Content Daily Word Quiz: acquiesce Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language