/ Dictionary / Index D day one: Meaning and Definition of Find definitions for: day' one' Pronunciation: [key] (often caps.) the very first day or beginning of something. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Day of the Lord daypack Related Content Daily Word Quiz: digression Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language