(1)唯一的，仅有的(without any others of the same type doing the same thing，etc)[作attrib]：He has no brothers or sisters — he's an～child.他没有兄弟姐妹，是独生子。This is the～book of its kind in the world.这是世界上这类书的孤本。He was the～person who came to see me.他是唯一来看我的人。〖同〗lone，sole，alone，unique;〖反〗many，several，numerous;

(2)最好(适合的)(so good that there is no other possible choice)(infml)：Running is the～way to keep fit.跑步是保持健康的最好方法。He's the～man for the position.他是担任这个职位的最佳人选。