Blue blood - Idioms

blue blood

Comes from the medieval belief that aristocratic blood was blue. Usually used talking about nobelty and royal family members.

There's too much blue blood in this family! They really should mix with the common people otherwise they'll degenerate...

"Blue blood" is an English idiomatic phrase for "noble birth."

 the expression blue blood does not mean that blood is blue, but it means to belong to a royal family.