<p><strong>Plural Noun</strong></p><ul><li>Archaea</li></ul><p><strong>Definition</strong></p><ul><li>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.</li><li>Considered to be an ancient form of life that evolved separately from bacteria and algae and classified as constituting the domain Archaea.</li></ul>