Ordovician period or·do·vi·cianperiod uncommon noun 1. from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds SynonymsOrdovicianOrdovician period Related words Broader terms period Parts Paleozoic WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.
