双尾词，也称为元音双尾词，是指英语单词中包含两个元音字母，并且这两个元音字母位于单词的中间位置。例如，单词 "fair" 就是一个双尾词，因为它包含两个元音字母 "a" 和 "i"，它们位于单词的中间。
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