Cousin Terms and Definitions
Your first cousin is a child of your aunt or uncle. You share one set of grandparents with your first cousin, but you do not have the same parents.
Your second cousin is the grandchild of your great-aunt or great-uncle. You share one set of great-grandparents with your second cousin, but you do not have the same grandparents.
Third, Fourth, and Fifth Cousins
Your third cousin is the great-grandchild of your great-great-aunt or great-great-uncle. You share a set of great-great-grandparents with your third cousin, but do not have the same great-grandparents. Fourth cousins have one set of great-great-great-grandparents, but not the same great-great-grandparents. And so on.
If two siblings in one family marry two siblings from another family and each couple has a child, the children are double first cousins. The word double in addition to the first cousin term is because they share the same four grandparents. Regular first cousins share only one set of common grandparents, while double first cousins share both sets of grandparents plus all lineal and collateral relatives.
The relationships of cousins of different generations are explained by using the word “removed”. Cousins who are “once removed” have a one-generation difference. For example, the first cousin of your father is your first cousin, once removed. In that case, your father’s first cousin is one generation younger than your grandparents and you are two generations younger than your grandparents. This one-generation difference is explained by saying that you are cousins “once removed.”. Removed cousin relationships are never measured by age, but only by generation differences.
Twice removed means that there is a two-generation difference between cousins. If you are two generations younger than the first cousin of your grandparent, then the relationship between you and your grandparent’s first cousin are first cousins, twice removed.
Cousin relationships can be any combination of first, second, third and so on, with once removed, twice removed, and so on. A genealogy program will calculate exact family relationships in your family tree for both blood relatives and relatives by marriage.