Si·lu·ri·an 
(sĭ-lrē-ən, sī-)
(sĭ-lrē-ən, sī-)adj.
Of, relating to, or being the period of geologic time from about 444 to 416 million years ago, the third period of the Paleozoic Era. The Silurian Period is characterized by the development of jawed fishes, invertebrate land animals, and land plants. See Table at geologic time.
n.
The Silurian Period.
[From Latin Silures, an ancient people of southwest Wales, where the rocks were first identified.]