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
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.
The masculine equivalent of "niece" is "nephew." A nephew is the son of one's sibling or sibling-in-law. While "niece" refers specifically to a female relative, "nephew" serves the same familial role but for males.
Niece would be the female counterpart for a nephew.
Male niece is female
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.
nephew in yoruba