ar·chae·or·nis \ˌärkēˈȯrnə̇s\noun Etymology: New Latin, from archae- + -ornis 1.capitalized: a genus of Upper Jurassic birds (subclass Archaeornithes) having a long feathered tail, showing reptilian characteristics in the absence of a bill, presence of teeth in the jaws, and on the wings three free digits with claws 2.-es: a bird or fossil of the genus Archaeornis