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”; archaeo- ( def. )

Origin of Archaea²

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

Example Sentences

These tiny organisms form the base of the marine food chain, meaning the activity of ammonia-oxidizing archaea ultimately helps sustain ocean biodiversity.

From Science Daily • Mar. 11, 2026

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

From Science Daily • Mar. 11, 2026

Their results indicated that despite inhibiting these ammonia oxidizers -- mostly archaea that are abundant in the dark ocean -- the rate of carbon fixation in the study areas didn't drop as much as expected.

From Science Daily • Dec. 10, 2025

If ammonia-oxidizing archaea are not responsible for as much carbon fixation as once believed, other microbes must be stepping in.

From Science Daily • Dec. 10, 2025

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