yellow dog Informal
n.1. A mean or contemptible person or thing.
2. A staunchly loyal member of the Democratic Party who consistently supports other Democrats.
[From Southern regional yaller dog, yellow dog, mongrel dog with a yellowish coat, cowardly dog. Sense 2, so called because it was said that such Democrats would vote for the party's candidate even if it nominated a yaller dog.]
yellow-dog′ adj.