Definition of archaean

• a. - Ancient; pertaining to the earliest period in geological history.
• n. - 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.
• a. - Ancient; pertaining to the earliest period in geological history.
• n. - 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.