only

1. Origins, structure, and basic meaning

• Structure: 唯 conveys being the only one and is read ゆい in the words here.
• Basic usage: 唯一 is read ゆいいつ, and 唯一無二 is read ゆいいつむに.

2. Common pitfalls and similar expressions

• The scope of being unique
  • 祖父が残した唯一の記念品 means the only keepsake left by one's grandfather. The preceding description sets the scope within which it is the only one.
  • 私にとって唯一無二の宝物 means a one-of-a-kind treasure to me. It also identifies the person for whom the treasure has incomparable value.