Two people with the same great uncle may be first cousins or second cousins to each other, or may not be related to each other at all. It depends on whether the great uncle is the brother of a grandparent, or the husband of a sister of a grandparent.
He would be your great-great uncle.
No, there is nothing wrong with it. People are not likely to be able to figure out that there is any relationship, and if the great great uncle is from the "other side" of your grandchild's family, he is not related to you at all.
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.
The English language recognizes no relationship between you and your husband's great uncle.
Your great uncle is the brother of one of your grandparents. If you are a boy, you are your great uncle's great nephew. If you are a girl, you are your great uncle's great niece.
Your grandmother's brother is your great uncle. You and your great uncle's grandchild are second cousins to each other. Your and your great uncle's great grandson are second cousins, once removed.
Your great uncle's daughter would be your aunt.
Your Great Uncle is your the brother of one of your grandparents, and therefore the uncle of one of your parents.
Your uncle is your child's great uncle. Your child is his great niece (if a girl) or great nephew (if a boy).
Your grandfather's uncle is your great uncle.
your uncle is your sons great uncle
Your 3rd cousin