(n)a major North American river and the chief river of the United States; rises in northern Minnesota and flows southward into the Gulf of Mexico, Syn.Mississippi River
prop. n. 1. A geological period extending from from 310 million to 345 million years ago; it was associated with an increase of land areas, the presence of primitive ammonites, and emergence of winged insects; called also Missippian period and Lower Carboniferous period. Syn. -- Missippian period, Lower Carboniferous, Lower Carboniferous period. [ WordNet 1.5 ]