Aunt, Uncle, Niece, Nephew

There are standard words for collateral relationships, where neither person is directly descended from the other. B0 and C0 are brother and sister, or more generically siblings. Going down one generation, on one side only, we have four common relationships:

• B0 is C1‘s uncle. Most English speakers use “uncle” for any of four relationships: father’s brother, mother’s brother, father’s sister’s husband, or mother’s sister’s husband.
• C0 is B1‘s aunt. Again, “aunt” in English could mean your father’s sister, mother’s sister, father’s brother’s wife, or mother’s brother’s wife. Most people would say Z0 is also C1‘s aunt.
• C1 is the niece or nephew of B0; most people would say C1 is also the niece or nephew of Z0.

Children of your aunt or uncle are your first cousins. More generally, B1 and C1, and all their descendants, are cousins to each other. A separate section below details all the words used to describe cousin relationships.