/ Dictionary / Index M modacrylic fiber: Meaning and Definition of Find definitions for: mod'a•cryl'ic fi'ber Pronunciation: (mod'u-kril'ik, mod"-), [key] any of various synthetic copolymer textile fibers, as Dynel, containing less than 85 percent but more than 35 percent of acrylonitrile. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. mod modal Related Content Daily Word Quiz: secular Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language