also: ゆいつむに
noun which may take the genitive case particle 'no', na-adjective, noun
one and only; unique; unparalleled
Emphasizes absolute uniqueness; there is nothing else like it. Often used in formal or emphatic contexts.
彼は私にとって唯一無二の親友だ。
He is my one and only best friend.
この作品は唯一無二の価値がある。
This work has unparalleled value.