The idiom "blue blood" refers to someone who comes from a noble or aristocratic family. It is believed that the term originated from the fact that the veins of people with fair skin, such as those of noble birth, appear blue.
You can use this idiom to describe someone who has a high social status due to their family background. For example, you might say, "She may not have any experience in politics, but her blue blood will certainly help her get elected."
It's important to note that this idiom is not commonly used in everyday conversation and is more often found in literature or historical contexts.
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