Wiktionary
greyback
n. 1 (context historical US colloquial English) A Confederate soldier during the US Civil War (because of the grey uniforms). 2 (context dated English) A louse. 3 A local name for various grey birds.
Usage examples of "greyback".
For the same reason that Avery, Yaxley, the Carrows, Greyback, Lucius" — he inclined his head slightly to Narcissa — "and many others did not attempt to find him.
For the same reason that Avery, Yaxley, the Carrows, Greyback, Lucius" ?
The dolphins all seemed to know Greyback and crowded around, nibbling affectionately at his flukes and flippers.