/ Dictionary / Index S sidereal day: Meaning and Definition of Find definitions for: side'real day' Pronunciation: [key] — Astron. Astron. the interval between two successive passages of the vernal equinox over the meridian, being about four minutes shorter than a mean solar day. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. sidereal sidereal hour angle Related Content Daily Word Quiz: feral Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language