Legionnaires' disease

noun

Le·​gion·​naires' disease ˌlē-jə-ˈnerz- How to pronounce Legionnaires' disease (audio)
variants or less commonly Legionnaire's disease
: pneumonia that is caused by a bacterium (Legionella pneumophila), is characterized initially by symptoms resembling influenza (as malaise, headache, and muscular aches) followed by high fever, cough, diarrhea, severe pneumonia, and mental confusion, and that may be fatal especially in elderly and immunocompromised individuals

Examples of Legionnaires' disease in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
From bed bugs to asbestos to now Legionnaires' disease — since returning to the office, California state workers have faced many issues. — Carmela Karcher, CBS News, 14 July 2026 Symptoms of Legionnaires' disease Those with symptoms who have been in the area are urged to receive medical attention promptly. — Amethyst Martinez, USA Today, 10 July 2026 Although most people recover from Legionnaires' disease with antibiotics, certain patients – including those who are immunocompromised or who suffer from chronic lung diseases – can develop complications that can be fatal. — Mary Kekatos, ABC News, 9 July 2026 See All Example Sentences for Legionnaires' disease

Word History

Etymology

from its first recognized occurrence at an American Legion convention in 1976

First Known Use

1976, in the meaning defined above

Time Traveler
The first known use of Legionnaires' disease was in 1976

Rhymes for Legionnaires' disease

See All Rhymes for Legionnaires' disease

Browse Nearby Words

legionnaire
Legionnaires' disease
Legion of Honor
See all Nearby Words

Cite this Entry

“Legionnaires' disease.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/Legionnaires%27%20disease. Accessed 15 Jul. 2026.

Copy Citation

Medical Definition

Legionnaires' disease

noun
variants also Legionnaire's disease
: pneumonia that is caused by a bacterium of the genus Legionella (L. pneumophila), that is characterized initially by symptoms resembling influenza (as malaise, headache, and muscular aches) followed by high fever, cough, diarrhea, lobar pneumonia, and mental confusion, and that may be fatal especially in elderly and immunocompromised individuals see pontiac fever

More from Merriam-Webster on Legionnaires' disease

Britannica.com: Encyclopedia article about Legionnaires' disease

Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Popular in Grammar & Usage

See More

Merriam-Webster’s Great Big List of Words You Love to Hate

Is that lie 'bald-faced' or 'bold-faced'?

'A' or 'an'? What about before 'h'? An Indefinite Article Guide

Why is '-ed' sometimes pronounced at the end of a word?

Commonly Misspelled Words
See More

Popular in Wordplay

See More

14 Phobias You Probably Haven't Heard Of

It's a Scorcher! Words for the Summer Heat

The Longest Long Words List

Ten Words Ending with a Silent ‘T’

12 Lovely and Unusual Words for the Natural World
See More

Popular

See More

Merriam-Webster’s Great Big List of Words You Love to Hate

14 Phobias You Probably Haven't Heard Of

It's a Scorcher! Words for the Summer Heat
See More

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
The Missing Letter A daily crossword with a twist
banana-mirrored
Contradictory Words Quiz Pick out which word means one thing…and the opp...
See All