WordNet sense 1 (`Johnny' was applied as a nickname for Confederate soldiers by the Federal soldiers in the American Civil War; `greyback' derived from their grey Confederate uniforms):

rebel, Johnny, Reb, rebel, Johnny Reb

WordNet sense 2 (a dowitcher with a grey back):

grayback, Limnodromus griseus

WordNet sense 3 (a sandpiper that breeds in the arctic and winters in the southern hemisphere):

knot, Calidris canutus