*brontozoum*

‖n. [ NL., fr. Gr. &unr_; thunder + &unr_; animal. ] (Paleon.) An extinct animal of large size, known from its three-toed footprints in Mesozoic sandstone. [ 1913 Webster ]

☞ The tracks made by these reptiles are found eighteen inches in length, and were formerly referred to gigantic birds; but the discovery of large bipedal three-toed dinosaurs has suggested that they were made by those reptiles. [ 1913 Webster ]