/ Dictionary / Index S sun gear: Meaning and Definition of Find definitions for: sun' gear" Pronunciation: [key] — Mach. Mach. (in an epicyclic train) the central gear around which the planet gears revolve. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Sungari Sunghua Related Content Daily Word Quiz: paradox Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language