noun.
A genus of huge fossil dinosaurian reptiles, notable for their small head and diminutive brain-cavity, the whole skull not exceeding some of the neck-bones in size. One species was about 50 feet long, and probably weighed 20 tons or more.
the GNU version of the Collaborative International Dictionary of English
noun.
A genus of large sauropod American dinosaurs of the jurassic era, or an individual of that genus. A length of sixty feet is believed to have been attained by these reptiles. The genus is also called Apatosaurus, and individuals of the genus are also called brontosaurs.