In addition to Takkat’s answer, I want to remark that we should focus on helping users to understand what a tag is about, not on explaining the word behind the tag.
The purpose of tag wikis is to explain the usage of a tag. Thus focus on such things as:
- To what questions should this tag be applied?
- To what questions should this tag not be applied?
- Are there related tags that may be better suited?
In most cases we do not need to educate the user what the word behind a tag means. For example most users know what a verb is and in the rare case that they don’t, there are better places to explain it to them, in particular Wikipedia. The exception are highly technical terms such as expletiva, but even here a short description usually suffices.
Finally, remember that the excerpt usually suffices to store all the information required for most purposes and you only need the actual wiki if the usage of a tag needs extensive information or if you want to give guidance on how to ask a good question in a given tag or list good example questions.