blue blood

1. Noble or aristocratic descent.
2. A member of the aristocracy.

[Translation of Spanish sangre azul : sangre, blood + azul, blue (probably from the visible veins of fair-complexioned aristocrats).]

noun

1. Noble rank or status by birth: birth, blood, nobility, noblesse. See kin, over/under.
2. People of the highest social level: aristocracy, crème de la crème, elite, flower, gentility, gentry, nobility, patriciate, quality, society, upper class, who's who. Informal upper crust. See over/under.

Former enlisted Marine who crossed over and accepted a commission. See Mustang.