Ordovician

a.

1.

(Geol.) Of or pertaining to a division of the Silurian formation, corresponding in general to the Lower Silurian of most authors, exclusive of the Cambrian.

Noun

1.

Ordovician - from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds Synonyms: Ordovician period

geological period, Ordovician period, Paleozoic, Paleozoic era, period