To your uncle, you are his niece or nephew.
Your father's uncle is your great uncle. You are his great niece or great nephew.
Your nephew's son is your great nephew. You are his great aunt if you are female, or his great uncle if you are male.
If you are a girl, you are a niece to you aunt and uncle. If you are a boy, you are their nephew.
your nephew to your father is grandpa
Cousin.
Uncle is to aunt as father is to mother.
Sister-in-law describes a female. Brother-in-law describes a male.
The opposite relationship of uncle would be Niece or Nephew.(The opposite gender is aunt.)
The son of your aunt and uncle is your first cousin.
If your aunt has a brother who is not your uncle, then your aunt is the wife of one of your parent's brothers, and that aunt's brother is no relation to you.
Great great aunt/uncle. To your niece, you are the aunt/uncle, to her child you would be the great aunt/uncle. So you would then be the great great aunt/uncle of her child's child (her grandson)
Your niece will call you her aunt or uncle.
In spanish, aunt is tia and uncle is tio.
I saw your aunt and uncle
Your uncle's sister is your aunt, or possibly your mother.
In Portuguese aunt is spelled Tia (you pronounce it chia) and uncle is tio(you pronounce it chi-o)
Your uncle's wife is your aunt.