Breadcrumb Home > Dictionary > Index F firmament: Meaning and Definition of Find definitions for: fir•ma•ment Pronunciation: (fûr'mu-munt), [key] — n. the vault of heaven; sky. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: firmament (Thesaurus) firm firman ✖ Related Content Daily Word Quiz: derogate Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language