An animal having a greyish back. US. Any of several wading birds; especially the (red) knot, Calidris canutus, in winter plumage.
The (greater) scaup, Aythya marila.
A louse. Also figurative.
More fully "greyback whale". The grey whale, Eschrichtius robustus.
More fully "greyback crow". The hooded crow, Corvus corone cornix. Compare grey crow.
A member of a military or police force whose uniform includes, or consists of, a grey coat; specifically (US, informal) a soldier of the Confederate army in the American Civil War (1861–5). Compare greycoat, "grey".
A monetary note issued by the Confederacy during the American Civil War. Compare "blueback", "greenback".