1. Any of various extinct, often gigantic, carnivorous or herbivorous reptiles of the orders Saurischia and Ornithischia that were chiefly terrestrial and existed during the Mesozoic Era. 2. A relic of the past: "living dinosaurs of the world of vegetation" (John Olmsted). 3. One that is hopelessly outmoded or unwieldy: "Anyone who interprets the bible literally is a dinosaur" (Peggy Breault).