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