a. [ Gr. 'archai^os ancient, fr. 'archh` beginning. ] Ancient; pertaining to the earliest period in geological history. [ 1913 Webster ]

n. (Geol.) 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. [ 1913 Webster ]

☞ This is equivalent to the formerly accepted term Azoic, and to the Eozoic of Dawson. [ 1913 Webster ]