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n. pl. ar·chae·a (-kē-ə)
Any of various prokaryotic microorganisms of the domain Archaea, being genetically distinct from bacteria and often living in habitats with extreme environmental conditions such as high temperature or salinity. Also called archaebacterium.

[New Latin Archaeon (back-formed singular of Archaea, domain name), from Greek arkhaion, neuter singular of arkhaios, ancient (in reference to the very ancient separation of the archaea and the eubacteria in evolutionary history); see archaic.]


an order of prokaryotic microorganisms
References in periodicals archive ?
The icy orb known as Enceladus may boast ideal living conditions for single-celled microorganisms known as archaeans found in some of the most extreme environments on Earth, they reported in the science journal Nature Communications.
27) covers salt-lovers and other types of archaeans, and Rona Arato's PROTISTS (9780778753773, $29.
The molecular sequence data that underlie the three domains, based on a few ribosomal genes, find that archaeans are more closely related to eukaryotes than to bacteria.