词典释义：
释义
n.
a thing that is needed in order to complete a series, provide continuity, or gain complete knowledge
（系列关联事物中）缺少的一环
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she is the missing link between the European ballad tradition and Anglo-American white soul. 在欧洲传统民谣和英美白人爵士灵乐之间她起了承上启下的作用。
a hypothetical fossil form intermediate between two living forms, especially between humans and apes
缺环（指介于两种生命形式，尤指人类和类人猿之间的假想化石形态）。