In genealogy, your first cousin’s children have a specific name: they are your first cousins once removed. This term, which is often unfamiliar, refers to people who share the same great-grandparents as you.
In everyday speech, they are sometimes called “second cousins” or even treated as nieces or nephews, but these labels do not correspond to any legal or genealogical relationship. The bond between you sits at the intersection of three distinct systems: family usage, genealogical terminology and French civil law.
First cousins once removed: a frequently misunderstood sixth degree of kinship under civil law
Under French civil law, the degree of kinship is calculated using a simple principle: count up from yourself to the common ancestor, then back down to the other person, counting each generation but not the ancestor themselves. Between you and your first cousin’s children, the common ancestors are a couple of grandparents (for your cousin) or great-grandparents (for their children).
In practical terms, the path goes up three generations (you, your parent, your grandparent), then down three generations (your cousin’s parent, your cousin, their child). That makes six degrees of kinship under civil law.
This calculation differs from canon law, which is still used in religious genealogy and counts only the number of generations between the common ancestor and the more distant person. Under this system, the same relationship is considered third degree. If you consult an old family tree or church document, the numbering will be different—that is often where the confusion comes from.
To put this relationship into perspective, my cousin’s son is in exactly the same genealogical position as my cousin’s daughter: both are first cousins once removed, at the sixth degree under civil law.
Everyday language and genealogical terminology: why families get it wrong
Few families use the expression “first cousin once removed” in everyday life. Three imprecise terms are commonly used instead.
- “Second cousin” is the most common term, but it has no official definition under French law. It can refer to a first cousin once removed or to a more distant cousin.
- Some families call a close cousin’s children “nieces” or “nephews,” especially when there is a significant age difference. This is an affectionate label, not a kinship relationship: a niece or nephew is strictly the child of a sibling.
- Others simply say “cousin,” without specifying the degree, which keeps family gatherings in a state of perpetual confusion.
This confusion is not merely a matter of terminology. It can cause real problems after a death, when a certificate of inheritance must be drawn up or the order of heirs established. Notaries apply the civil-law calculation, not family custom.
The special case of cousins by marriage
If your cousin is not related to you by blood but by marriage (their spouse is your first cousin), their children are not your first cousins once removed. They are your cousins by marriage, a relationship that does not create any degree of kinship under the French Civil Code. This distinction has direct consequences for inheritance: a cousin by marriage does not inherit under the rules of intestate succession.
Inheritance and degree of kinship: what the sixth degree means in practice
The degree of kinship is not just a matter of genealogical curiosity. Under French law, it determines whether you can inherit from someone who dies without a will. Heirs are divided into classes (descendants, ascendants, privileged collateral relatives and ordinary collateral relatives), and within each class, the closest degree of kinship takes precedence.
First cousins once removed fall into the category of ordinary collateral relatives in the sixth degree. If there are no descendants, ascendants or privileged collateral relatives (siblings and their descendants), they may inherit. The presence of heirs in a higher-priority class excludes them from the estate, even if they were emotionally close to the deceased.
French law allows collateral relatives to inherit up to and including the sixth degree. Your first cousin’s children are therefore at the limit of this threshold. Beyond that, if there is no will, the estate goes to the state.
Degree of kinship and inheritance tax
Even when a first cousin once removed inherits (usually under a will), the tax burden is high. Inheritance tax between people without a direct family relationship is charged at the highest rates. A will can leave property to a distant cousin, but the tax bill significantly reduces the net amount received.
Family tree: visualizing the relationship between first cousins once removed
The best way to clear up any ambiguity is to map the relationship on a family tree, even a simple one. Start with your shared great-grandparents and follow the two separate branches.
- Branch 1: great-grandparents, grandparent (your side), your parent, you.
- Branch 2: great-grandparents, grandparent (your cousin’s side), your cousin’s parent, your cousin, their child.
- The branches meet at the couple of great-grandparents and split at the next generation.
This diagram shows that each additional generation adds a degree of kinship and makes the relationship more distant. Your first cousin’s children are more distantly related to you than your cousin is (fourth degree), and even more distantly related than your aunt or uncle (third degree).
Genealogical terminology also has terms for later generations: the children of two first cousins once removed are “second cousins once removed,” at the eighth degree under civil law. At this point, there is no longer any legal right to inherit without a will.
The relationship with your cousin’s children can be summed up in one sentence: you share great-grandparents, you are related in the sixth degree under civil law, and the law recognizes you as collateral relatives. Anything beyond that—affectionate nicknames or feeling like their aunt or uncle—is part of your lived family relationship, not the law.
