plural noun

ar·​chaea är-ˈkē-ə How to pronounce archaea (audio)
: usually single-celled, prokaryotic microorganisms of a domain (Archaea) that includes methanogens and those of harsh environments (such as acidic hot springs, hypersaline lakes, and deep-sea hydrothermal vents) which obtain energy from a variety of sources (such as carbon dioxide, acetate, ammonia, sulfur, or sunlight)
Characterized under the heading archaea, these creatures have an amazing lineage that extends deep in the geologic record to the twilight of Earth's organic origins.Todd Wilkinson
… although archaea organize their DNA much as bacteria do (they also have no cell nucleus, for example), many aspects of the way the DNA gets processed are distinctly different. Instead, the processing is more similar to what goes in within eukaryotic cells.Olivia Judson
Many of the archaea are thermophilic. These amazing "extremophiles" eke out a living in environments in which no other organism can survive.David W. Wolfe
see archaean compare bacterium, eukaryote
archaeal adjective
Hot springs in Yellowstone National Park have revealed head-spinning levels of archaeal diversity—including a pair of organisms that are the most primitive forms of life alive today. Carl Zimmer
… the archaeal proteins responsible for several crucial cellular processes have a distinct structure from the proteins that perform the same tasks in bacteria. W. Ford Doolittle

Examples of archaea in a Sentence

Recent Examples on the Web The University of Hawaii is conducting further tests to learn more about the archaea. Rebecca Carballo, New York Times, 11 Nov. 2023 Cloning is much simpler, and for a long time, many scientists thought the common ancestor of all eukaryotes—the branch of life that includes animals, plants, fungi, slime mold, and everything else besides bacteria and the small, strange archaea—took that route. Ilana E. Strauss, The Atlantic, 11 Nov. 2020 Some of the most important genes that shaped the evolution of the early eukaryotes have changed so much that they can’t be ascribed to either archaea or bacteria. Ed Yong, Discover Magazine, 13 Sep. 2010 This internal organisation sets the eukaryotes apart from the two other domains of life: the prolific bacteria; and the archaea, masters of extreme environments. Ed Yong, Discover Magazine, 13 Sep. 2010 If the archaea are in there, more nitrite will start to appear. Melina Walling, The Arizona Republic, 3 Oct. 2022 The Dunaliella dies and the archaea and bacteria take over. Jennifer Billock, Smithsonian Magazine, 13 June 2022 That’s because microbes like bacteria and archaea coat surfaces in a sticky layer, a biofilm, that functions as a chemical and physical come-hither call for larger creatures such as barnacles and coral, Dr. Hamdan said. Katherine Kornei, New York Times, 21 Feb. 2020 Collectively, this consortium of bacteria, archaea, fungi and viruses are called our microbiota. Michelle Sconce Massaquoi, The Conversation, 3 Mar. 2020 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'archaea.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


New Latin, from Greek archaios

First Known Use

1990, in the meaning defined above

Time Traveler
The first known use of archaea was in 1990

Dictionary Entries Near archaea

Cite this Entry

“Archaea.” Dictionary, Merriam-Webster, Accessed 7 Dec. 2023.

Kids Definition


noun plural
ar·​chaea är-ˈkē-ə How to pronounce archaea (audio)
: single-celled organisms that are prokaryotes often of harsh environments (as hot springs) and include forms that produce methane

Medical Definition


noun plural
ar·​chaea är-ˈkē-ə How to pronounce archaea (audio)
capitalized : a domain of primitive single-celled prokaryotic microorganisms including methane-producing forms and others that thrive in extremely salty or hot, often acidic environments
They are largely Archaea, a domain of life first identified 20 years ago …Charles W. Petit and Laura Tangley, U.S. News & World Report
: microorganisms of the domain Archaea
Many of the archaea are thermophilic.David W. Wolfe, Wilson Quarterly
archaeal adjective
Despite the morphological resemblance of archaea to bacterial cells (e.g., lack of a nuclear membrane), many archaeal processes, such as transcription, are much more similar to those of eukaryotes. Ken F. Jarrell, Bioscience

More from Merriam-Webster on archaea

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