also: ニェット
interjection
Russian loanword used as an interjection; often carries a blunt or emphatic tone, similar to a firm refusal or denial.
from Russian nyet
「手伝ってくれない？」「ニエット！」
"Won't you help me?" "Nyet!"
彼は質問にニエットとだけ答えた。
He answered the question with just a "nyet."