以下二个句子中，as均为引导比较分句的从属关联词，只不过从句作了省略。

As always, he said little.

=As he always did, he said little.

The 'h' in honest is silent, as in 'hour'.

= The 'h' in honest is silent, as it is in 'hour'.

至于as引导比较分句时是什么词类，网友就不必追究了。主流语法认为as是连词，但有人认为是代词或副词。比如牛津就把这里的as分析为副词。