Pronunciation: (ôr"du-vish'un), [key] Geol.
noting or pertaining to a geologic period of the Paleozoic Era, from 500 million to 425 million years ago, notable for the advent of fish. See table at geologic time.
the Ordovician Period or System.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.