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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 ?
When they looked through a microscope at a type of archaeum known generally as Ignicoccus, they noticed some smaller, spherical objects attached to it.
At first, the scientists thought they were observing a virus on the archaeum.
a novel hyperthermophilic archaeum that oxidizes [Fe.