archaea

¹ American  

[ahr-kee-uh] / ˈɑr ki ə /

plural noun

Microbiology.

singular

archaeon

1. a group of microorganisms, including the methanogens and certain halophiles and thermoacidophiles, that have RNA sequences, coenzymes, and a cell wall composition that are different from all other organisms: considered to be an ancient form of life that evolved separately from bacteria and algae and classified as constituting the domain Archaea.

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Archaea ² American  

[ahr-kee-uh] / ˈɑr ki ə /

noun

(used with a singular or plural verb)

1. (in the three-domain system of classification) the taxonomic domain comprising the archaea.

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Etymology

Origin of archaea¹

First recorded in 1985–90; from New Latin, from Greek archaîa, neuter plural of archaîos “ancient”; see origin at archaeo- ( def. )

Origin of Archaea²

First recorded in 1990–95; from New Latin; see origin at archaea ( def. )

Example Sentences

These archaea oxidize ammonia, a process that plays a central role in the ocean's nitrogen cycle.

From Science Daily • Mar. 11, 2026

"These Asgard archaea are often missed by low-coverage sequencing," said co-author Kathryn Appler, a postdoctoral researcher at the Institut Pasteur in Paris, France.

From Science Daily • Feb. 20, 2026

Writing in the journal Nature, the team focused on a group of microbes called Asgard archaea, which are considered close relatives of the ancestors of complex life.

From Science Daily • Feb. 20, 2026

As of the 1970's, however, microbiologists no longer consider archaea bacteria, but classify them as a separate domain in all life forms.

From Science Daily • May 1, 2024

Their study, published in Nature Communications, shows that these archaea are very 'picky eaters', which might drive their hosts to change the menu.

From Science Daily • May 1, 2024