Your sister's (or brother's) son is your nephew. You are his aunt or uncle.
You are each others cousins.
She's you're american horse pet.
Your nephew's first cousin may or may not be related to you, depending on how the cousin is related to your nephew. Your nephew's cousin may be your child, or the child of one of your brothers or sisters. Your nephew is related to you by being the son of your sibling. That sibling has a spouse who may also have borthers and sisters. The children of any of those brothers and sisters are also your nephew's first cousins, but are not related to you.
Uncle or Auntie.
Your sister's son is your nephew and you are his aunt (if you are female) or his uncle (if you are male.
Daughter
sisters are people who are related
Your sister's son is your nephew.
No, making your son wear his sisters pants is not a good punishment.
Cousin
He is your cousin
nephew