chla·​myd·​ia klə-ˈmi-dē-ə How to pronounce chlamydia (audio)
plural chlamydiae klə-ˈmi-dē-ˌē How to pronounce chlamydia (audio)
: any of a genus (Chlamydia, family Chlamydiaceae) of spherical gram-negative intracellular bacteria
especially : one (C. trachomatis) that causes or is associated with various diseases of the eye and urogenital tract including trachoma, lymphogranuloma venereum, cervicitis, and some forms of urethritis
: a disease or infection caused by chlamydiae
chlamydial adjective

Example Sentences

Recent Examples on the Web For example, 27-year-olds in 2017 had the same positive chlamydia test rate as 24-year-olds did in 2010, according to the study. Christen A. Johnson,, 22 Sep. 2020 Evofem is planning to start a pivotal study of the gel for the potential prevention of chlamydia and gonorrhea in women later this year, which could also boost its appeal to users and investors. Fortune, 22 May 2020 As of mid-2019, Cepheid’s GeneXpert system was cleared to test multiple types of samples for chlamydia, gonorrhea, and trichomoniasis. Mark Hay, Fortune, 21 Apr. 2020 This is the first clinical trial for a vaccine for genital chlamydia and represents the latest development in 15 years of research, according to an SSI statement. Jack Guy, CNN, 13 Aug. 2019 Research into vaccines against herpes and HIV is advanced, while immunizations for chlamydia, gonorrhea, syphilis and trichomoniasis, another common STI, are in earlier stages of development. Jason Gale | Bloomberg, Washington Post, 19 July 2019 STIs like herpes, gonorrhea, chlamydia, and mycoplasma can also infect and irritate the urethra, the Mayo Clinic explains (so treating the STI could potentially address your UTI as well). Patia Braithwaite, SELF, 3 Feb. 2020 And, as De Gabriele notes, other factors aside from fire play into the dwindling koala population—including chlamydia (which results in infertility), other wildlife attacks, and the effects climate change is having on eucalyptus trees themselves. Claire Gallam, Condé Nast Traveler, 11 Feb. 2020 Kangaroo Island is one of few places in the country where koalas have largely been untouched by chlamydia. Jennifer Leman, Popular Mechanics, 13 Jan. 2020 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'chlamydia.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History


borrowed from New Latin, originally the name of a group, from Greek chlamyd-, chlamýs "mantle, chlamys" + New Latin -ia -ia entry 1

Note: The taxon Chlamydia was originally assigned to a group of microorganisms neither bacterial nor viral by Helen Jones, Geoffrey Rake, and Barbara Stearns in "Studies on lymphogranuloma venereum III. The action of the sulfonamides on the agent of lymphogranuloma venereum," Journal of Infectious Diseases, vol. 76, issue 1 (January, 1945), pp. 55-69. The choice of the element chlamyd- was presumably based on the earlier taxon Chlamydozoa (with -zoa -zoa) originated by Ludwig Halberstädter and Stanislaus von Prowazek, "Über Zelleinschlüsse parasitärer Natur beim Trachom," Arbeiten aus dem Kaiserlichen Gesundheitsamte, vol. 26, Heft 1 (1907), pp. 44-47.

First Known Use

1966, in the meaning defined at sense 1

Time Traveler
The first known use of chlamydia was in 1966

Dictionary Entries Near chlamydia

Cite this Entry

“Chlamydia.” Dictionary, Merriam-Webster, Accessed 5 Dec. 2022.

Medical Definition



chla·​myd·​ia klə-ˈmid-ē-ə How to pronounce chlamydia (audio)
capitalized : the type genus of the family Chlamydiaceae comprising coccoid to spherical gram-negative intracellular parasitic bacteria and including one (C. trachomatis) that causes or is associated with various diseases of the eye and genitourinary tract including trachoma, lymphogranuloma venereum, cervicitis, and some forms of nongonococcal urethritis
plural chlamydiae -ē-ˌē, -ˌī How to pronounce chlamydia (audio) also chlamydias
: a bacterium of the genus Chlamydia
: an infection or disease caused by a bacterium of the genus Chlamydia
chlamydial adjective

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