Your father or another uncle.
The brother of your aunt's husband is not your uncle. Also the brother of your uncle who is not your uncle is your father.
Your mother's brother is your uncle.
Your uncle is the brother of one of your parents. Your great uncle is the brother of one of your grandparents. Your great great uncle is the brother of one of your great grandparents.
It depends on how he's your uncle. If he's your uncle because he's your father's brother, his brother is also your uncle. Or your father. If he's your uncle because he's your mother's brother, his brother is also your uncle. If he's your uncle because he's married to your mother's or father's sister, his brother is pretty much "no relation" to you, or at least English does not have a specific phrase for the relationship that's more concise than "uncle's brother".
Your grandfather's brother is your great uncle and your parent's uncle.
Your mother's brother is your uncle. Your uncle's brother-in-law is either the husband of his sister or the brother of his wife. The brother of your uncle's wife is not related to you. The husband of your uncle's sister is either your father, or the husband of another one of your mother's sisters and thus your uncle.
Setä = Father's brother (uncle) Eno = Mother's brother (uncle)
Your mom's brother to your child is a great uncle. That is because your mom's brother is YOUR uncle, so he to your child will be a great uncle!
Your relation to your mums uncle is GREAT uncle. You're welcome! 
Your father's brother is your uncle. English does not have different names for a father's elder and younger brother. If you are a boy, you are your uncle's nephew; if you are a girl, you are his niece.
Your mother's brother is your uncle. Your uncle is your son's great uncle. You are the nephew of your mother's brother. Your son is his great nephew.
your great uncle your grandmother's brother is your parent's uncle.... and confusingly enough when your parent is related to someone of the generation older than them (their uncle) it becomes your (great uncle) great relative.