1. extinct reptile: an extinct, chiefly terrestrial reptile that lived in the Mesozoic Era. Some dinosaurs were the largest known land animals. Order Ornithischia, Saurischia.
2. outmoded person or thing: somebody or something that is hopelessly out of date or incapable of adapting to change
[Mid-19th century. < modern Latin dinosaurus< Greek deinos "terrible" + sauros "lizard"]
