Any reptile of the extinct order (or suborder) Aetosauria, known from fossil remains of the Triassic period, and comprising herbivorous diapsids that resembled heavily armoured crocodiles.
Late 19th century; earliest use found in Isaac Funk (1839–1912), publisher and reformer. From scientific Latin A?tosaurus, genus name from ancient Greek ?ετ?? eagle (from the same Indo-European base as classical Latin avis bird + ancient Greek -ετ??, suffix forming nouns) + scientific Latin -saurus.