Have you any idea who a “second cousin, once removed” is? I did not know and have done some research. Let’s see if I can pass it on.
The definition of a first cousin is something most seem to grasp readily: You are the first cousin of the child of any aunt or uncle (who is the sibling of either of your parents). You share two of your four grandparents with each of your first cousins.
When we use the term second cousin (or third, fourth, etc.), we are describing people who are at the same generational level in relation to their ancestors. The same is true for third cousins, fourth cousins, etc.; they must always be at the same generational level.
So, if A is the mother and B and C are her children, B and C represent the same generation. (Throughout, when we refer to generations in these illustrations, it will always be relative to A.) If B and C have children, B¹ and C¹, respectively, B¹ and C¹ are first cousins. Again, they are of the same generation.
Next B¹ and C¹ each has a child, B² and C², respectively; B² and C² are again of the same generation (great grandchildren of A) and, in relationship to each other, they are second cousins. If B² and C² have children, B³ and C³, B³ and C³ are of the same generation (great, great grandchildren of A), and they are third cousins. This continues indefinitely. (For the sake of simplicity and clarity, each of our alphabet people has only one child, except for A who has two. Real life is never that simple.)
People at different generational levels (such as uncle and his niece) can never be first, second, third cousins, except by adding appendages, such as once removed, twice removed, or thrice removed which are used to designate relatives of different generations.
For purposes, of clarity, even though it may be repetitious, in our illustration A is first generation; B and C (as children of A) are second generation; B¹ and C¹ (as grandchildren of A) are third generation; B² and C² (as great grandchildren of A) are fourth generation; and so it goes. If the little numbers of the alphabet people are the same, they are of the same generation.
Using only alphabet people from above, B¹ and C¹ are first cousins (the children of siblings B and C). B¹’s child, B², and C¹ are still considered to be first cousins, but now they are first cousins, once removed (i.e., B² is a generation below C¹). Quite simply, the child of my first cousin is still my first cousin, but once removed. When B² has a child, B³, the relationship of “first cousin” between C¹ and B³ is preserved (because B³ is directly descended from B¹ who is C¹’s first cousin); but because B³ is now two generations below C¹, they are first cousins, twice removed.
Now you have the principles; putting our alphabet people to work again, who would be second cousins, once removed? We know that B² and C² are both of the fourth generation, and we know (from above) that they are second cousins; going to the next generation then we find that C³ (fifth generation) and B² (fourth generation) are second cousins, once removed, as are B³ and C². Continuing, C4 is the second cousin, twice removed of B².
Stay with it; it all makes sense.
Because family lineage tends to spread out very quickly with each generation, it can be challenging, but less so if you create a chart. (Imagine my family: My parents had eight children; 28 grandchildren; and, 30 great grandchildren.). Go back up a generation or two in your own family, chart it, and see where it leads; who is what in relation to others. (Too complex for Jeopardy?)
– Ken Butera