двоюродный

Etymology
From +. is a genitive dual form, from which was extracted and used analogously in,.

Usage notes

 * There is no single equivalent of this term in English. It is applied to close relations (e.g. brothers, uncles, grandfathers) and indicates a relation that is in the same generation as the term being modified, but is one degree greater in separation in terms of the closest common ancestor. For example, the двою́родный equivalent of one's brother is one's first cousin, because one has a common father with one's brother, but a common grandfather with one's first cousin. Similarly, the двою́родный equivalent of one's grandfather is one's great uncle, because the nearest common ancestor between one and one's grandfather is the grandfather himself, whereas the nearest common ancestor between one and one's great uncle is one's great-grandfather. (The двою́родный equivalent of one's father is one's uncle, but there is already a special term for this relationship.)