/ Dictionary / Index M myofibril: Meaning and Definition of Find definitions for: my•o•fi•bril Pronunciation: (mī"u-fī'brul, -fib'rul), [key] — n. Cell Biol. a contractile fibril of skeletal muscle, composed mainly of actin and myosin. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: myofibril (Thesaurus) myoelectric myofilament Related Content Daily Word Quiz: censure Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language