Tyrannosaurus rex /taɪˌɹænəˈsɔːɹəs ˈɹɛks/ noun1 •A giant carnivorous theropod dinosaur from the Cretaceous period.Some of the most spectacular beasts in East Coast museums happen to be Tyrannosaurus rexes from Montana. — 1999 formsTyrannosauri reges · Tyrannosaurus Rexes · Tyrannosaurus rexes · tyrannosaurus rexes