/ Dictionary / Index S spiral galaxy: Meaning and Definition of Find definitions for: spi'ral gal'axy Pronunciation: [key] — Astron. Astron. a galaxy having a spiral structure. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. spiral casing spiral gear Related Content Daily Word Quiz: penchant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language