Webster's 1913 Dictionary
ARCHAEAN
Ar *chæ "an, a. Etym: [Gr.
Defn: Ancient; pertaining to the earliest period in geological history.
ARCHAEAN
ARCHAEAN Ar *chæ "an, n. (Geol.)
Defn: The earliest period in geological period, extending up to the Lower Silurian. It includes an Azoic age, previous to the appearance of life, and an Eozoic age, including the earliest forms of life.
Note: This is equivalent to the formerly accepted term Azoic, and to the Eozoic of Dawson.
New American Oxford Dictionary
archaea
ar chae a |ärˈkēə ɑrˈkiə | ▶plural noun another term for archaebacteria. DERIVATIVES ar chae an (also archaeal ) adjective & noun
Archaean
Ar chae an ▶adjective British spelling of Archean.
Oxford Dictionary
archaea
archaea |ɑːˈkiːə | ▶plural noun Biology microorganisms which are similar to bacteria in size and simplicity of structure but radically different in molecular organization. They are now believed to constitute an ancient group which is intermediate between the bacteria and eukaryotes. Also called archaebacteria. DERIVATIVES archaean (also archaeal ) adjective & noun ORIGIN modern Latin (plural ), from Greek arkhaios ‘primitive ’.
Archaean
Archaean |ɑːˈkiːən |(US Archean ) ▶adjective Geology relating to or denoting the aeon that constitutes the earlier (or middle ) part of the Precambrian, in which there was no life on the earth. It precedes the Proterozoic aeon and (in some schemes ) is preceded by the Priscoan aeon. Also called the Azoic. • (as noun the Archaean ) the Archaean aeon or the system of rocks deposited during it. The Archaean extended from the origin of the earth (see Precambrian ) to about 2,500 million years ago. In schemes which include the Priscoan aeon, the Archaean began about 4,000 million years ago. ORIGIN late 19th cent.: from Greek arkhaios ‘ancient ’ + -an .
The Wordsmith Dictionary