Question

Is first lady a proper noun?

Answer 1

It depends on the use of those words. See explanation.

Explanation:

It is a proper noun when you mean one exact person, then you should use capital letter:

First Lady of the United States - Michelle Obama.

But if you refer not to one person, but to the idea of the first lady without mentioning a name then you treat it as a common noun and you do not have to write it with captal letters.

For example: Should the first lady earn a salary? In this sentence you think about any person not an actual one.