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A Cousin is a relative with whom one shares a common grandparent or more distant ancestor, and who is not in one's own line of descent. The term cousin, never applies where there are other specific terms to describe relationships.

If someone walked up to you and said "Howdy, I'm your third cousin, twice removed, "would you have any idea what they meant? Most people have a good understanding of basic relationship words such as "mother," "father," "aunt," "uncle," "brother," and "sister." But what about the relationship terms that we don't use in everyday speech? Terms like "second cousin" and "first cousin," once removed? We don't tend to speak about our relationship in such exact terms ("cousin" seems good enough when you are introducing one person to another), so most of us aren't familiar with what these words mean.

RelationshipTerms :
Cousin (a.k.a "first cousin")
Your first cousins are the people in your family who have two the same grandparents as you. In other words, they are the children of your aunts and uncles.

Second Cousin
Your second counsins are the people in your family who have the same great-grandparents as you, but not the same grandparents.

Third, Fourth, and Fifth Cousins
Your third cousins have the same great-great-grandparents, fourth cousins have the same great-great-great-grandparents, and so on.

Removed
When the word "remove" is used to describe a relationship, it indicates that the two people are from different generations. You and your first cousins are in the same generation (two generations younger than your grandparents), so the word "removed" is not used to describe your relationship.

The word "once removed" mean that there is a difference of one generation. For example, your mother's first cousin is your first cousin, once removed. This is because your mother's first cousin is one generation younger than your grandparents and you are two generations younger than your grandparents. This one-generation difference equals "once removed."

Twice removed means that there is a two-generation difference. You are two generations younger than a first cousin of your grandmother, so you and your grandmother's first cousin are first cousin twice removed.

Cross Cousin
A cousin who is the child of one's mother's brother or one's father's sister.

Parallel Cousin
A cousin who is the child of one's mother's sister or one's father's brother. Parallel cousins are the children of two brothers or two sisters.

Double Cousins
If two in one family marry two sisters from another, and each couple has a child, the offspring are double cousins. The addition of the word double to the first cousin term is the result of the number of common grandparents that are shared in this case. Regular first cousins share only one set of common ancestors, while double first cousin share all lineal and collateral relatives.

Kissing Cousin
A distant relative known well enough to be kissed when greeted, cousin marriage.