What is the X in X-mas?
1879, Modern Latin, from Greek bronte "thunder" (perhaps from PIE imitative root *bhrem- "to growl") + -saurus. Brontes was the name of one of the Cyclopes in Greek mythology.
A large herbivorous (see herbivore) dinosaur, perhaps the most familiar of the dinosaurs. The scientific name has recently been changed to Apatosaurus, but Brontosaurus is still used popularly. The word is from the Greek, meaning “thunder lizard.”