While a "nephew" refers to a male child of your sibling, a "niece" would refer to a female child of your sibling. Both are related to you in the same way, and would call you "Uncle" if you are a male, or "Aunt" if you are a female.
Niece would be an opposite as a niece is female and a nephew is male.
Nephew is the opposite of cousin
NIECE
The opposite gender noun for "nephew" is "niece." A nephew is the son of one's sibling, while a niece is the daughter of one's sibling. Both terms refer to the same familial relationship but differ based on gender.
Niece would be an opposite as a niece is female and a nephew is male.
In English cousin denotes a family relationship, it is not gender specific.
The opposite relationship of uncle would be Niece or Nephew.(The opposite gender is aunt.)
neice
The feminine opposite of nephew is niece.
There is no "opposite" of a nephew, unless you say that since a nephew is male, the opposite is a niece, who is female.
niece
niece