Ordovician

from WordNet (r) 3.0 (2006)

Ordovician
    n 1: from 500 million to 425 million years ago; conodonts and
         ostracods and algae and seaweeds [syn: {Ordovician},
         {Ordovician period}]

from The Collaborative International Dictionary of English v.0.48

Ordovician \Or`do*vi"cian\, a. [From L. Ordovices, a Celtic
   people in Wales.] (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. -- n. The Ordovician
   formation.
   [1913 Webster]