/ Dictionary / Index M myasthenia: Meaning and Definition of Find definitions for: my•as•the•ni•a Pronunciation: (mī"us-thē'nē-u), [key] — n. Pathol. muscle weakness. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: myasthenia (Thesaurus) myasis myasthenia gravis Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language