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First ... second ... third cousins
once ... twice removed

Cousins share a common ancestor at least two generations back.

First cousins have one pair of grandparents in common. For example:

specimen family tree

Peter Jones is [first] cousin to Adam and Susan Smith because they share grandparents John and Ann Smith

Walter Smith is second cousin to Lucy and Rebecca Jones because they share great-grandparents but not grandparents.

Joseph Smith is third cousin to Rachel Williams because they share great-great-grandparents ...

Fourth cousins would share a pair of great-great-great-grandparents

And so on.





When a cousin is described as 'once removed' it means that one of the cousins is a generation further away from the common ancestor than the other. For example:

specimen family tree

Peter Jones is first cousin to Adam Smith.

Peter's children Lucy and Rebecca also have Adam Smith as a first cousin, but in their case the relationship is 'once removed' because they are one more generation away from the common ancestors than Adam.

Lucy's daughter Rachel is also first cousin to Adam Smith, but now the relationship is 'twice removed'.

So the children, grandchildren, great-grandchildren, etc, of your first cousin are also your first cousins, once removed, twice removed, and three times removed respectively.