/ Dictionary / Index S sign-in: Meaning and Definition of Find definitions for: sign-in Pronunciation: (sīn'in"), [key] — n. an act, an instance, or a time of signing in. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: sign-in (Thesaurus) signifying signior Related Content Daily Word Quiz: cosmology Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language