/ Dictionary / Index F fibrillation: Meaning and Definition of Find definitions for: fi•bril•la•tion Pronunciation: (fī"bru-lā'shun, or, esp. for 2, fib"ru-), [key] — n. the formation of fibrils. uncontrolled twitching or quivering of muscular fibrils. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: fibrillation (Thesaurus) fibrillate fibrilliform Related Content Daily Word Quiz: candor Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language