Your grandmother's sister is your great aunt. (Some would say grand aunt).
Your great aunts' grandchild is your second cousin. Her great grandchild is your second cousin, once removed.
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Of course she is. The two of you share a common ancestor in one or two of your great great grandparents.
The granddaughter of your great grandmother's sister is your second cousin, once removed.
First cousins once removed. They would be your parent's cousin.
The great granddaughter of your great grandmother's sister is your third cousin.
The great-grandchild of your grandmother's sister is your second cousin, once removed.
Your grandmother's sister's child is the first cousin of one of your parents, and you first cousin once removed.
Second cousins
You are second cousins once removed.
Your grandmother's sister is your great aunt.
You grandmother's half-sister is your half-grandaunt.
Your grandmother's sister's daughter's grandson is your second cousin, once removed.
Your grandmother's sister is your great aunt. You are her great niece, if you are a girl, or her great nephew, if you are a boy.
Your mother's mother is your grandmother. Your grandmother's sister is your great aunt, and your mother's aunt.
The grandchild of your great grandmother's sister is your second cousin, once removed.
Your grandmother's sister is your great aunt. Her son's child is her grandchild. You and your great aunt's grandchild are second cousins.
Your great grandmother's sister is your great great aunt and you are her great great niece (if you are female) or great great nephew (if you are make).
Your great great grandmother's sister is your great great grandaunt, some would say great great greataunt.
Your grandmother's sisters daughter is your parent's first cousin, and your first cousin, once removed.
Your grandmother's sister's grandchildren are your second cousins.
You are second cousins once removed.