/ Dictionary / Index L legionnaires' disease: Meaning and Definition of Find definitions for: legionnaires'' disease" Pronunciation: [key] — Pathol. Pathol. a type of acute pneumonia caused by Legionella pneumophila bacterium and characterized by fever, chest pain, cough, and muscle aches. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. legionnaire Legion of Honor Related Content Daily Word Quiz: frugal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language