The daughter of a person's brother or sister is that person's Niece
The son of a person's brother or sister is that person's nephew
A nephew is the son of one's sibling, brother-in-law, or sister-in-law.
They are referred to as a niece.
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.
In English there are no masculine or feminine forms. English uses gender specific nouns for a male or a female. The noun nephew is a word for a male relative; the noun niece is a word for a female relative.
You are your nephew's uncle if you are male, and his aunt if you are female.
Niece would be an opposite as a niece is female and a nephew is male.
Male niece is female
Niece would be the female counterpart for a nephew.
There is no "opposite" of a nephew, unless you say that since a nephew is male, the opposite is a niece, who is female.
The female nephew is called the neice.
a nephew
You are her niece or nephew (niece if female, nephew if male) and she is your aunt.
female.male.
Your father's brother is your uncle. You are his niece (if you are female) or his nephew (if you are male).