The definition of a first cousin is the son or daughter of one of your parent's siblings.
An example of a first cousin is your aunt's child.
(plural first cousins)
- Starting with two first cousins (two persons with a common grandparent), the relationship between one of those persons and the offspring of the other is first cousin once removed.
- The relationship between one of those persons and the grandchild of the other is first cousin twice removed.