Your daughter is your uncle's grand niece.
Since your uncle's sister is your aunt, her daughter would be your cousin, just as your uncle's daughter would be.
Your mother's brother is you uncle and your daughter's great uncle. Your daughter is his great niece.
She is his great grandniece.
their aunt or uncle
I guess you will be her uncle. Consider this case.. You have a brother and he has a daughter.. Your daughter will be a sister in law to your brother's daughter.
Being your sister's brother or sister you would be an uncle or an aunt to her daughter.
Your nephew's daughter is your great niece and you are her great Aunt (or Great Uncle).Correction:Your nephew's daughter is your grand niece. You are her grand aunt or grand uncle.
You are the great aunt/uncle of your sister's son's daughter, and your sister's son's daughter is your great niece.
Your grandmother's brother is your great uncle. Your great uncle's grandchildren are your second cousins.
There is no direct connection, only one of marriage. She is your niece. You are her uncle.
first cousin, once removed.
There is no relation between you, and your biological Uncle's wife's sibling's daughter. Your Uncle's wife is technically an "Aunt in law", though as routine courtesy is simply called "Aunt". Her brother/sister, if your family and her family are that close, could be regarded as an "Uncle/Aunt in law", as a stretch. Thus the daughter of him/her could be thought of as a "cousin in law" to you. But this is all a matter of courtesy, there is no biological or legal relation.