/ Dictionary / Index E ephemeris second: Meaning and Definition of Find definitions for: ephem'eris sec'ond Pronunciation: [key] — Astron. Astron. the unit of ephemeris time, defined as a precise fraction of the length of the tropical year 1900. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ephemeris ephemeris time Related Content Daily Word Quiz: neologism Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language