1.
unique; peerless; matchless; one and only
Having no equal or duplicate; something or someone so special that there is no second.
Literally means "without a second" — 無 (without/none) + 二 (two/second). The word expresses the idea that something is so exceptional that there is nothing else like it.
Most commonly encountered in the four-character compound 唯一無二 (one and only; absolutely unique), which is widely used in both spoken and written Japanese. On its own, 無二 appears primarily in the set phrase 無二の親友 (irreplaceable best friend) and in literary contexts.