/ahr'kee bak tear"ee euh/ , n. pl., sing. archaebacterium /-tear"ee euhm/ .
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 the bacteria and blue-green algae and sometimes classified as a kingdom.
Also, archaeobacteria /ahr'kee oh bak tear"ee euh/ .
[ 1977; archae-, irreg. for archaeo- ARCHAEO- (perh. an erroneous Latinizing of Gk arche- ARCHE-) + bacteria BACTERIA ]