/ Dictionary / Index P planet gear: Meaning and Definition of Find definitions for: plan'et gear" Pronunciation: [key] — Mach. Mach. any of the gears in an epicyclic train surrounding and engaging with the sun gear. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. planetesimal planetoid 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