What does 其 add to 尤其?
No. As you can see in the dictionary, 尤 must be used with another word, or other words, to form a phrase that means something. For example, it has the meaning of &quot;particular&quot; when used in the phrase &quot;對計算機尤感興趣歐&quot;. However, in the phrase &quot;尤物&quot;, its meaning changed to &quot;rare&quot;, &quot;exceptional&quot;.
其, depending on the use, can be translated as &quot;its&quot;, &quot;such&quot;, &quot;that&quot;. Similar to 尤, it must be used with other words to be meaningful. As shown in the dictionary, it means &quot;especially&quot; when in the phrase &quot;尤其重要&quot;, and means &quot;particular&quot; in &quot;尤其是綠茶&quot;.
Thus, the following phrases are false:

尤重要

其重要

尤是綠茶

其是綠茶