1. A group of single-celled microorganisms that are genetically distinct from bacteria and often live in extreme environments such as hot springs, salt lakes, or deep ocean vents.
Usage: Also called archaea (modern preferred term); Scientific/biological context; Plural: archaebacteria or archaebacterium

Examples

• Archaebacteria were discovered in the 1970s and were initially thought to be bacteria.
• Many archaebacteria thrive in environments with extreme temperatures that would kill most other organisms.
• Scientists study archaebacteria to understand the origins of life on Earth.
• Some archaebacteria produce methane gas as a byproduct of their metabolism.
• The cell membranes of archaebacteria differ significantly from those of true bacteria.
• Archaebacteria are now classified as a separate domain of life called Archaea.