I have a big family—my dad was one of six, and my mother had fifteen siblings who grew to adults, with another two who died young and three to five others lost in pregnancy and birth. So I have over fifty first cousins and tons more out along the family line!
It’s hard keeping track, but we’re lucky in one respect—my grandparents had just the one marriage for all those children. Therefore, they are all full siblings, and no half or steps to consider in the immediate group.
But it’s not always that easy—particularly in this current world—and I’ve seen a lot of minor errors and inconsistencies about who is a half vs a step vs a full sibling.
So I’d like to encourage authors—and readers!—to think about some of those differences.
A full sibling has the same parents as you.
A half sibling is one that has the same mother (or father) and a different father (or mother). Or at least they share half your bloodline.
A step sibling is one who is related through the marriage of a parent, but doesn’t have a blood relationship to you.
Oddly, Merriam-Webster uses a space and often no hyphen with half, but one word for step—all the steps (stepfather, stepmother, stepsister, stepbrother, stepsibling). Sometimes grammar is odd, and the treatment goes one way and doesn’t match what we think it should!
As for other relationships…
A first cousin means that you have a common grandparent.
A second cousin means that you have a common great-grandparent.
A third cousin means that you have a common great-great-grandparent.
And so on.
And the removed is the closes to a common relative, and then the generations away.
So your father’s first cousin, is your first cousin once removed.
Your father’s first cousin’s child is your second cousin—and that child is also your father’s first cousin once removed. (His connection to the common relative is first, hers is one lower)
Your first cousin’s child is your first cousin once removed.
It does seem hard to follow at first but the interest in ancestry has shown some great sites that explain the intricacies of all this!
So if you’re a cousin, Slainte!
How do you keep track of them all?