The "cousin" relationship is always one more then the common "great" ancestor relationship, so people with a common 3 x great-grandparent would be 4th cousins to each other. (3 greats + 1 = 4th cousins)
Simple? Just remember:
*1st cousins always share a common grandparent (0 great=1st)
* 2nd cousins always share a common great-grandparent (1 great=2nd)
* 3rd cousins always share a common 2nd great-grandparent (2 great=3rd)
* 4th cousins always share a common 3rd great-grandparent. (3 great=4th)
etc.
*1st, 2nd, 3rd, etc. Cousins are always of the same generation.
*Cousins NOT of the same generation are cousins "removed".
The number of times a cousin is "removed" depends on the number of generations "away" they are.
Example:
"1st cousin once removed" being the child of your 1st cousin.
"1st cousin twice removed" being the grandchild of your 1st cousin.
*This is true of PRECEDING generations of cousins as well.
(Though not with 1st cousins since their parents and grandparents would be aunt/uncles and grandparents)
Example: While the child of your "2nd Cousin" is your "2nd Cousin once removed" (being one generation "removed" from yours).....
the parent of your "2nd cousin" is ALSO your "2nd cousin once removed" because they are one generation "removed" from your generation as well.
*Someone who is a 1st cousin to any of your direct lineage family members.....(persons you directly descend from your grandparents, your great-grandparents, etc.) is a 1st cousin to you, but are "removed", of course.
Example: The "1st cousin" of your great-grandparent is:
"1st cousin once removed" to your grandparent
"1st cousin twice removed" to your parent
"1st cousin thrice removed" to you
"1st cousin 4 times removed" to your child and so on.
