Priscoan (iou)

Priscoan adjective & noun. L20.
[Irreg. from Latin priscus ancient + -AN.]
Geology.
A. adjective. Of, relating to, or denoting the aeon that (in some schemes) constitutes the earliest part of the Precambrian, extending from the origin of the earth to the beginning of the Archaean aeon about 4,000 million years ago, and which has left no identifiable rocks. L20.
b. noun. The Priscoan aeon. L20.