Definition of archaebacteria in US English:


plural noun

  • Microorganisms that are similar to bacteria in size and simplicity of structure but radically different in molecular organization. They are now believed to constitute an ancient intermediate group between the bacteria and eukaryotes.

    Also called archaea
    • ‘These sequences included proteins from a diverse range of organisms, ranging from eubacteria and archaebacteria to algae, fungi, and plants.’
    • ‘The most startling (and, for some people, unbelievable) such event was the origin of the eukaryotes by the fusion of an archaebacterium with some eubacteria.’
    • ‘They conjecture that an evolutionary quantum leap happened after an archaebacterium swallowed a eubacterium.’
    • ‘What's more, these origin-of-life researchers suspect that the two major groups of bacteria, known as archaebacteria and eubacteria, originated on two separate occasions about 3.8 billion years ago.’
    • ‘These ‘bugs, ‘actually archaebacteria, thrive in intense heat and pressure deep underground, without any light - that is, in a truly alien environment within planet earth.’’


1970s: modern Latin (plural), from Greek arkhaios ‘primitive’.