An uncle is the brother of one of your parents, or the husband of the sister of one of your parents.
A nephew is the son of your sister or brother.
An uncle's nephew and the uncle's child are first cousins to each other. The uncle's great granddaughter and the nephew are first cousins twice removed to each other.
it great nephew :)
You are his uncle, he is your nephew.
To your uncle, you are his niece or nephew.
There is no difference between a great nephew and a grand nephew. In some places "great nephew" is the preferred term for the grandson of one of your siblings. In other palces, grand nephew" is the preferred term for that relationship.
Your uncle's nephew could be you (if you are a boy), or your brother, or your first cousin. Your uncle's nephew could also be unrelated to you if he is the son of a sibling of your uncle's wife.
You are your nephew's uncle, or aunt, and his son's great uncle, or great aunt. Your nephew's son is your great nephew.
You would be a neice or nephew, neice if a girl and nephew if a guy.
You would be his uncle and he would be your nephew.
You are a great great Aunt (or Uncle) to the grandson of your Nephew.
Your brother's (or your sister's) son is your nephew and you are his aunt if you are a female or his uncle if you are a male.
The English language has no specific term for a relationship between your uncle and your wife. Your uncle will usually call her "my nephew's wife" and she can call him "my husband's uncle."