- Ordovician⇄adj. of the Ordovician or its rocks.
- Ordovician⇄noun 1. a geological period, the second in the Paleozoic era, after the Cambrian and before the Silurian. The Ordovician is characterized by the first appearance of vertebrates and the development of many trilobites, brachiopods, and other invertebrates.
- Ordovician⇄Ordovician, noun, adjective.