Ordovician, ca.
(Of Ordovices, ancient tribe of North Wales).
1. adj. Géol. Said of the second period of the Paleozoic era spanning from makes 500 million years ago to 440 million years ago, characterized by the abundance of invertebrates and the emergence of the first terrestrial plants and vertebrates. U t. c. s. m.
OrRTOGR. ESCR. with may. initial c. s.
