breed of dog known for its charmingly sad expression and beautiful coat, which is long, silky, and very feathery; coat may be black and tan, solid red, red and white, or tricolor; feathery ears hang quite long and to the side of the head; tail is usually not docked and is feathery with some white at the tip; eye color is dark; adult stands 12–13 in. (30–33 cm) tall at shoulders and weighs 10–18 lbs (5–8 kg); originated in Great Britain and, after years of mixed breeding, revived again in 1920s; Princess Margaret of England acquired one in the 1960s and the breed's popularity soared.