/ Dictionary / Index F fastness: Meaning and Definition of Find definitions for: fast•ness Pronunciation: (fast'nis, fäst'-), [key] — n. a secure or fortified place; stronghold: a mountain fastness. the state of being fixed or firm: the fastness of democratic institutions. the state of being rapid. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: fastness (Thesaurus) fast-moving Fast of Esther Related Content Daily Word Quiz: resilient Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language