[ ˌɔ:də'vɪʃɪən ]
■ adjective Geology relating to or denoting the second period of the Palaeozoic era (between the Cambrian and Silurian periods, about 510 to 439 million years ago), a time when the first vertebrates appeared.
Origin
C19: from Ordovices , the L. name of an ancient British tribe, + -ian .