The Collaborative International Dictionary of English v.0.48:

Rosella \Ro"sel"la\, n. [NL., dim. of L. rosa rose.] (Zool.)
   A beautiful Australian parrakeet (Platycercus eximius)
   often kept as a cage bird. The head and back of the neck are
   scarlet, the throat is white, the back dark green varied with
   lighter green, and the breast yellow.
   [1913 Webster]