1 one of two children or animals that are born to one mother at the same time 双胞胎或孪生子中的一个: They're very alike. Are they twins? 他们长得很像，是不是孪生儿？a twin brother/sister 孪生兄弟╱姐妹identical twins 单卵双胞胎 ☞Look at Siamese twin and triplet. 参看Siamese twin及triplet。

2 one of a pair of things that are the same or very similar 两个相同或非常相似的事物中的一个: twin engines 双引擎twin beds 成对的单人床 ☞Look at the note at bed ¹. 参看bed^1的注释。