ordovician period(n = noun.time) ordovician - from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds;
is a kind of geological period, period
is a part of paleozoic, paleozoic era

alabama period, cambrian period, carboniferous period, catskill period, champlain period, chemung period, class period, cretaceous period, devonian period, duty period, fertile period, final period, first period, geological period, gestation period, glacial period, hamilton period, historic period, historical period, incubation period, jurassic period, latency period, latent period, lower carboniferous period, lunar time period, lunch period, missippian period, neonatal period, niagara period, orbit period, ordovician, overtime period, pennsylvanian period, period, period of play, period of time, period piece, period style, permian period, playing period, precambrian period, quaternary period, reconstruction period, refractory period, rest period, safe period, salina period, second period, silurian period, tertiary period, test period, third period, time period, trenton period, trial period, triassic period, twenty-four hour period, upper carboniferous period