區別就是兩者意思上都可表示每個，具體的不同如下
each用於兩者或三者以上，中文意思是det. 每，各，每一，pron. 每個，各個，adj. 每個的，各自的，adv. 給每個，對各個
We drank a whole bottle each.
either one用於兩者，中文意思是兩者中的任何一者
The worker was bound to the master by a mutual contract that either one could repudiate， and the relationship was conceptualized as one of partnership.
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