WIERD QUESTION

Cousin

Not first cousins to each other.

I don't believe there's any common blood shared.

Unofficially I think that is cousins-by-marriage. In other words not a blood relative so it's not a 'real' relative.

Let's map it out. First off, I am going to assume you are not talking about a brother and sister. You are talking about people from opposite sides of the family, right? Because the truth is, my husband's sister has a son. That boy is nephew to both of us. But you are asking the relation between him and my brother's hypothetical daughter.

The answer is - there is no official relation whatsoever, at least not in English-speaking Western culture, that I am aware of.

There isn´t either on Spanish. Techinchally we called it something that is translated like "politic cousin". But is folklore, it is not an official spanish term.